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ELEMENTARY 
MACHINE  =SHOP.  PRACTICE 


AS  ADAPTED  TO  ITS  TEACHING  IN 

TECHNICAL    SCHOOLS 


By  T.  J.  PALMATEER 

INSTRUCTOR  IN  MACHINE  WORK 
Leland  Stanford  Junior  University 


Copyright  1918  by  T.  J.  PALMATEER 

1918 

Stanford  University  Press 


Library 


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DEPT 


PREFACE 

The  instructions  given  in  this  book  should  meet  the  require- 
ments of  beginners  in  general  machine  shop  practice.  The  main 
object  is  to  reduce  as  much  as  possible  the  time  required  to  bring  a 
student  with  no  previous  shop  experience  to  the  point  where  he  is 
able  to  do  some  real  work.  The  instructions  given  refer  mainly  to 
the  cutting  of  metal,  since  this  usually  gives  the  most  trouble  to 
beginners.  Little  attempt  has  been  made  to  describe  the  mechanism 
of  the  different  machines  because  it  varies  so  much  with  the  type 
and  make  and  is  besides  easily  understood  by  the  average  student. 

To  obtain  the  best  results  with  this  book  the  following  pro- 
cedure is  suggested.  In  most  cases  it  can  be  carried  out  without 
seriously  interfering  with  the  previously  established  work  of  the 
school : 

1.  The  instructor  should  give  practical  demonstrations  for  the 
different  exercises  and  actually  perform  those  operations  which  he 
considers  necessary. 

2.  The  student  should  study  the  instructions  given  herein  dur- 
ing his  leisure  time  before  and  after  the  demonstration. 

3.  Each  student  should  have  a  book  for  use  in  the  shop  so  that 
it  may  be  consulted  whenever  necessary.     This  will  help  to  develop 
initiative. 

4.  A  certain  amount  of  time  should  be  allowed  to  complete  the 
work.     This   should  be   enough  to  enable  the  average   student  to 
finish  on  time. 

Many  thanks  are  due  to  H.  P.  Miller,  Jr.,  for  his  helpful  assist- 
ance in  the  preparation  of  this  book  and  to  the  following  manu- 
facturers for  the  half-tone  illustrations :  Smith  &  Mills  Co.,  Sibley 
Machine  Co.,  and  the  Cincinnati  Milling  Machine  Co. 


T.  J.  PALMATEER. 


Stanford  University,  Cal. 
February,  1918. 


735782 


PART  I. 


LATHE  WORK 


ELEMENTARY     LATHE     PRACTICE. 


EXERCISE  No.  1 
FIT  SHAFT  TO  COLLAR— RUNNING  FIT 

Machine  Steel 


Cut  off  with  a  power  hack-saw  a  piece  of  steel  6  1/16  inches 
long  from  a  bar  1  inch  in  diameter.  This  will  allow  1/16  of  ari 
inch  for  finishing  the  ends  and  3/16  of  an  inch  for  turning  the 
diameter. 

An  experienced  lathe  operator  would  use  a  piece  of  steel  7/8 
of  an  inch  in  diameter,  but  for  beginners  it  is  better  to  use  larger 
stock  to  allow  for  pi?a<kice  -turning, 

•*  CENTERING 


Center  both  ends  in  the  centering  machine.  The  size  of  the 
center  in  this  shaft  should  be  from  3/16  to  1/4  of  an  inch  in 
diameter.  Larger  work  should  have  deeper  centers. 


,'Drill   and   Countersink 


Fig.  i 


ELEMENTARY    LATHE    PRACTICE. 


If  a  centering  machine  is  not  available,  the  work  may  be  cen- 
tered by  first  locating  the.  center  with  a  pair  of  dividers  and  cen- 
ter punch  and  then  using  a  combination  drill  and  countersink  in 
the  lathe  as  shown  in  Pig.  1.  In  this  case  the  work  is  held  by 
hand  to  prevent  it  from  turning.  As  this  work  is  to  be  turned,  it 
is  necessary  to  center  it  only  approximately  true. 

Accurate  Centering'. — When  the  work  is  to  be  centered  accur- 
ately, it  may  be  done  by  putting  one  end  in  the  lathe  chuck  and 
the  other  in  a  steady  rest.  A  pointed  tool  is  then  used  in  the  tool 
post  as  shown  in  Pig.  2.  The  po.nt  of  this  tool  has  an  angle  of  60 
degrees,  the  same  as  the  lathe  centers,  and  is  ground  like  a  flat 
drill  so  that  it  cuts  on  both  sides. 

After  the  shaft  is  centered  with  this  tool,  a  center  hole  about 
1/8  of  an  inch  in  diameter  should  be  drilled.  This  is  done  by 
holding  the  drill  in  the  tail-stock  of  tne  lathe  with  a  drill-chuck, 
as  shown  in  Fig.  3.  The  obj'.'c1:  of  this  <;ent<^  hole  is  to  give  the 
center  of  the  shaft  a  bearing  on  the  lathe  center  a  short  distance 
back  from  the  point,  as  at  A  in  Pig.  4. 

PLACING  WORK  IN  LATHE 

The  work  is  made  to  rotate  on  the  lathe  centers  by  fastening 
a  lathe  dog  to  the  shaft  at  the  head-stock  end,  as  shown  at  A  in 


Head   Stock 


Fig.  5 


Fig.  5. 

The  tail-stock  center  is  adjusted  so  that  the  shaft  Will  rotate 
freely,  yet  be  tight  enough  to  allow  no  slack,  or  lost  motion.  Since 
the  shaft  rotates  on  this  center,  it  should  be  kept  well  lubricated 
by  using  machine  oil,  or  a  mixture  of  graphite  and  oil. 

To  get  the  best  results  in  turning  th.s  sort  of  work,  it  is  neces- 
sary to  face  both  ends  before  turning  and  to  rough  turn  the  whole 
piece  to  within  about  0.03,  or  0.04  of  an  inch  of  the  finished  size 
before  any  part  of  it  is  finished.  However,  it  is  not  always  neces- 
sary to  do  this.  The  object  of  first  rough  turning  the  shaft  all 
over  is  to  remove  the  internal  strains  of  the  steel  and  to  wear  the 
centers  down  to  a  good  bearing  before  any  finshing  cuts  are 


ELEMENTARY     LATHE     PRACTICE. 


taken.    The  purpose  of  facing  the  ends  is  to  get  them  square,  or 
true,  and  smooth. 

FINISHING  END  OF  SHAFT 

To  face  the  ends,  use  a  regular  turning  tool  starting  to  cut 
from  the  outside  and  feeding  by  hand  towards  the  center  with  the 
cross  feed.  Such  a  tool  will  leave  a  ridge  near  the  center,  as 
shown  in  Fig.  6.  This  ridge  is  cut  off  with  a  sharp  pointed,  side 
cutting  tool,  as  shown  in  Fig.  7,  which  is  also  used  for  taking  the 


Fig.  6 


finishing  cut  across  the  whole  end  of  the  bar.  When  taking  this 
finishing  cut,  lard  oil,  or  some  other  lubricant,  should  be  used. 

After  the  finishing  cut  has  been  taken,  any  small  ridge,  or  fin 
that  remains  at  the  edge  of  the  center  is  removed  by  slightly 
changing  the  angle  of  the  tool  in  the  tool  post  and  allowing  about 
]  764  of  an  inch  play  between  the  centers.  Having  the  work  loose 
like  this  when  the  lathe  is  running,  allows  the  extreme  point  of 
the  side  tool  to  extend  beyond  the  edge  of  the  center  and  cut  a 
smooth  end. 

The  lathe  should  run  slow  for  the  finishing  cut  and  fast  when 
the  regular  turning  tool  is  used. 

TURNING  THE  SHAFT 

The  first,  or  roughing  cut,  is  taken  with  a  high  speed  steel 
tool,  or  bit,  fastened  in  a  tool  holder.  The  tool  holder  is  clamped 
in  the  tool  post  of  the  lathe  so  that  the  point  of  the  tool  is  at,  or 
a  little  above,  the  center,  or  axis,  of  the  lathe,  as  in  Fig.  8. 

If  the  point  of  the  bit  is  too  high,  it  is  easy  to  see  that,  as  the 
shaft  rotates,  the  tool  will  not  cut  at  all.  Fig.  9.  In  case  the  tool 
is  set  below  the  center,  the  cutting  action  is  very  poor  so  that 
turning  tools  are  never  set  as  in  Fig.  10. 


ELEMENTARY    LATHE    PRACTICE. 


Fig.  8 


fig.  9 


Pig  10 


Fig   II 

Turning     Tool 


Speed  of  the  Lathe. — In  taking  the  heavy  roughing  cuts,  the 
belt  may  be  placed  on  the  second  largest  step  of  the  cone,  while 
for  the  finishing  cuts  the  lathe  should  run  a  little  faster,  say  with 
the  belt  in  the  next  smaller  step. 

Grinding  Turning  Tool. — The  front,  or  point,  and  the  sides  of 
the  tool  are  ground  at  an  angle,  which  is  called  the  clearance.  If 
the  tool  has  too  little  clearance,  it  will  not  cut  freely,  while  if  it 
has  too  much  clearance,  the  point  will  be  so  thin  that  it  will  break 
off  or  become  dull  quickly. 

The  top  of  the  tool  is  also  ground  at  an  angle.  This  is  called 
the  rake.  If  the  tool  has  too  little  rake,  it  will  not  cut  freely  and 
if  it  has  too  much,  the  edge  will  soon  break  down. 

It  requires  some  practice  for  a  beginner  to  learn  the  proper 
rake  and  clearance  that  should  be  given  to  a  tool.  Fig.  11  shows 
a  tool  ground  with  clearance  and  rake  that  will  give  very  good 
results. 

Direction  Tool  Should  Travel. — The  depth  of  the  first  cut 
should  be  about  1/16  of  an  inch  and  the  travel  of  the  tool  should 
always  be  from  the  tail-stock  end  towards  the  head-stock.  If  the 
travel  is  in  the  opposite  direction,  the  pressure  on  the  tail-stock 
center  is  increased,  causing  it  to  heat  quickly. 

The  length  of  the  cut  should  be  as  great  as  possible  without 
the  lathe  dog  striking  the  tool,  or  cross-rest. 

Adjusting  the  Lathe  to  Turn  Straight. — After  the  first  cut, 
the  work  should  be  calipered  and  if  it  is  not  the  same  diameter 


ELEMENTARY     LATHE     PRACTICE. 


at  both  ends  the  tail-stock  should  be  adjusted  so  that  the  lathe 
will  turn  straight 

The  tail-stock  adjustment  is  made  by  loosening  the  main 
clamping  nut  B  and  one  of  the  screws  C  and  then  tightening  the 
other  screw  C  on  the  opposite  side  of  the  tail-stock,  Fig.  5. 

If  the  shaft  is  larger  at  the  tail-stock  end,  the  tail-stock  should 
be  moved  towards  the  front  of  the  lathe  one  half  the  difference 
between  the  diameters  of  the  shaft  at  the  two  ends. 

In  doing  close  work,  the  tail-stock  should  be  adjusted  as 
closely  as  possible,  but  in  this  case  if  it  is  off  center  only  a  little, 
say  0.002  or  0.003  of  an  inch,  it  will  be  close  enough  providing  it 
is  set  so  that  the  shaft  will  be  turned  larger  at  the  head-stock  end. 
If  the  tail-stock  is  set  so  that  the  shaft  is  turned  larger  at  the  tail- 
stock  end,  the  shaft  will  be  too  small  at  the  other  end  after  the 
finishing  cut  is  taken. 

Fitting  Shaft  to  the  Collar. — After  the  roughing  cut  is  taken 
and  the  lathe  has  been  adjusted  so  that  it  turns  approximately 
stra  ght,  the  end  of  the  shaft  is  turned  for  about  *4  of  an  inch  so 
that  it  w  11  just  fit  the  hole  in  the  collar,  shown  in  the  drawing 
of  Exercise  1.  To  measure  this:  first  set  the  inside  calipers  to  the 
d'ameter  of  the  hole  in  the  collar,  then  set  <he  outside  calipers  to 
the  inside  calipers  and  caliper  the  shaft  as  accurately  as  possible. 
For  a  final  test  of  this  diameter,  remove  the  work  from  the  lathe 
and  try  it  with  the  collar  itself. 

The  advantage  of  turning  but  %  of  an  inch  at  the  end  of  the 
shaft  is  this;  if  the  finishing  cut  were  set  too  deep,  only  y±  of  an 
inch  of  the  shaft  would  be  too  small,  while  if  this  cut  were  taken 
the  whole  length,  the  entire  shaft  would  be  too  small. 

After  the  shaft  has  been  turned  at  the  end  so  that  it  fits  the 
collar,  the  rest  of  the  shaft  should  be  turned  a  little  larger,  say 
0.002  or  0.003  of  an  inch,  in  diameter.  This  will  leave  enough  to 
finish  with  a  file. 

Filing. — The  object  of  filing  is  to  take  out  the  tool  marks,  but 
it  is  also  found  to  be  much  easier  to  make  a  close  fit  by  filing  off 
the  last  0.002  or  0.003  of  an  inch  than  to  take  so  small  a  cut  with 
a  tool.  The  amount  of  allowance  for  filing  depends  upon  the 
character  of  the  finishing  cut.  Since  the  less  filing  required  the 
better,  the  finishing  cut  should  be  made  as  smooth  as  possible. 

The  tool  used  for  the  roughing  cut  may  also  be  used  for  fin- 
ishing, but  it  is  usually  necessary  to  re-sharpen  it.  After  it  is  re- 
set in  the  tool  post,  the  point  should  be  flattened  a  little  wider 


10 


ELEMENTARY    LATHE    PRACTICE. 


than  the  pitch  of  the  feed,  say  about  1/32  of  an  inch,  and  parallel 
with  the  work.     This  is  done  with  an  oilstone. 

For  filing  work -on  a  lathe,  a  single  cut  file  is  used.  This  is 
called  a  lathe,  or  mill  file. 

u'^Ehe  stroke  of  the  file  should  be  slow,  steady,  and  straight 
across  the  shaft.  The  lathe  should  run  a  little  faster  for  filing 
than  for  turning,  the  object  being  to  have  the  work  make  several, 
revolutions  for  a  single  stroke  of  the  file.  If  the  lathe  runs  too^ 
slow  and  the  stroke  of  the  file  is  too  fast,  the  shaft,  instead  of 
be.ng  filed  round,  will  have  a  series  of  flat  places  on  the  surface. 

After  the  work  is  finished  as  close  to  the  dog  as  possible,  re 
verse  it  in  the  lathe  and  finish  that  part  where  the  dog  was  fast- 
ened. 


EXERCISE  No.  2. 


f 

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J"  Toper 

-1"  par  ft. 

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_J            _, 

4.  —  ' 

The  finished  shaft  in  Exercise  No.  1  may  be  used  for  Exercise  * 
>.  2. 

Place  the  shaft  in  the  bench  vise  and  with  a  rule  and  scriber 
ty  off  the  dimensions;   1%  iu-T  3  in.,  and  l1/^  in.     Then  center 
>unch  the  lines  just  deep  enough  so  that  they  can  be  easily  seen 
rhen  the  work  is  in  the  lathe. 
Turn  the  large  end  first. 
When  it  is  necessary  to  turn  a  fixed  distance,  or  to  a  line  a* 
in  this  case,  it  is  well  to  disconnect  the  feecT^flwm  the  tool  is  with- 
in about  1/8  of  an  inch  from  the  end  of  the  cut   and  to  feed  the 
tool  the  rest  of  the  distance  by  hand.    If  this  is  not  done,  the  tool 
may  travel  farther  than"  it  is  intended  to. 

It  is  better  to  turn  the  portions  to  be  threaded  a  little  under 
rather  than  over  size.  For  if  they  are  over  size,  the  threads  will 
not  fit  the  standard  size  nut,  but  if  under  size  the  threads  do  not 
need  to  be  cut  so  deep  in  order  to  fit  the  nut. 

For  measuring  the  diameters  of  this  piece  set  the  calipers  as 


ELEMENTARY     LATHE     PRACTICE. 


11 


accurately  as  possible  by  measuring  from  the  end  of  the  rule,  as 
shown  in  Fig.  12. 


Cutting1  Recess. — The  surface  at  the  end  as  well  as  the  recesses 
between  the  threads  and  the  taper  are  cut  with  a  square-nose,  or 
cutting-off  tool,  Fig.  13. 

This  tool  shoull  have  a  sharp  smooth  edge,  the  point  being  set 
level  with  the  center  of  the  lathe. 

To  produce  a  smooth  finished  surface  lard  oil  should  be  used 
with  a  slow  feed  and  lathe  speed. 

After  the  end  is  turned  to  size,  reverse  the  work  in  the  lathe 
and  turn  the  other  end  and  the  taper  before  cutting  the  threads. 

Turning  Taper. — The  drawing  calls  for  a  taper  of  1  inch  per 
foot.  This  is  cut  by  using  a  taper  attachment,  or  by  setting  the 
tail  stock  off  center.  As"  most  lathes  are  not  provided  with  a 
taper  attachment,  the  latter  method  will  be  used. 

If  the  worl$  was  12  inches  long,  the  tail  stock  would  be  mov^d 
off  center  1/2  inch  to  turn  a  taper  of  1  inch  per  foot.  It  being 
only  6  inches  Jong,  the  tail  stock  is  set  off  center  but  half  that 
amount,  or  14  inch. 

Before  taking  the  finishing  cut,  caliper  both  ends  to  prove 
that  the  lathe  is  cutting  the  correct  taper. 

THREAD  CUTTING 


The  threads  are  cut  to  fit  i/2  incn  and  5/8  inch 'nuts  having 
United  States  Standard  threads.     These  threads  are  flattened  at 
the  top  and  bottom  to  the  amount  of  1/8  of  the  pitch  instead  of 
eing  sharp  pointed  as  in  the  case  of  Standard  V-threads. 

Pitch. — The  pitch  of  the  thread  is  the  distance  from  the  center 
of  one  thread  to  the  center  of  the  one  adjoining.  On  the  end  of 
the  exercise  having  13  threads  per  inch  the  pitch  is  1/13  of  an 
inch  so  that  the  width  of  the  flat  at  the  top  and  bottom  of  this 


12 


ELEMENTARY    LATHE    PRACTICE. 


thread  should  be  1/8  of  1/13  of  an  inch,  or  about  .009  of  an  inch. 

Lead. — The  lead  of  the  thread  is  the  distance  a  nut  on  the 
screw  will  travel  in  making  one  complete  turn.  For  single  threads 
the  pitch  and  lead  are  the  same,  but  for  double  threads  the  lead 
is  twice  the  pitch. 

Grinding-  Tool. — The  sides  of  U.  S.  S.  threads  form  an  angle  of 
60  degrees.  To  cut  this  thread  in  a  lathe,  a  tool  the  same  shape  as 
the  threads  is  used.  A  gauge  for  grinding  this  tool  accurately  is 
shown  in  Pig.  14. 


fig.  14 


Fig  16 


If  a  U.  S.  S.  thread  gauge  is  not  available,  the  tool  can  be 
ground  with  the  aid  of  a  regular  thread  and  center  gauge,  shown 
in  Fig.  15.  With  such  a  gauge  the  angle  can  be  ground  accurate- 
ly, but  it  will  be  necessary  to  measure  the  flat  point  with  a  rule. 

The  top  of  the  tool  should  be  ground  so  that  it  will  be  approx- 
imately in  a  horizontal  plane  when  set  in  the  lathe. 

Where  the  thread  to  be  cut  is  as  fine  as  13  per  inch  the  flat 
surface  at  the  point  of  the  tool  is  so  small  that  the  extreme  point 
can  be  oil-stoned  off  instead  of  being  taken  off  with  the  grinding 
wheel.  The  flat  point  should  never  be  wider  than  the  standard 
size,  but  if  it  is  a  little  too  narrow  it  will  make  very  little  differ- 
ence in  ordinary  lathe  work. 

Setting  Tool. — To  set  the  tool  so  that  both  sides  of  the  thread 
will  have  the  same  angle,  the  thread  gauge  is  used  as  shown  in 
Fig.  16.  The  tool  should  be  set  on  a  level  with  the  center  of  the 
lathe. 

How  Lathe  is  Geared. — To  cut  13  threads  per  inch  the  work 
must  make  13  revolutions  while  the  carriage,  which  carries  the 
tool,  travels  one  inch.  For  this  purpose  the  lathe  spindle  is  con- 


ELEMENTARY     LATHE     PRACTICE. 


13 


nected  to  the  lead  screw  with  the  proper  size  gears  and  tfee  lead 
screw  to  the  carriage  by  a  split  nut.  This  split  nut  is  back  of  the 
carriage  apron  and  is  opened  and  closed  by  the  lever  E,  Fig.  17. 


If  the  lead  screw  of  the  lathe  has  6  threads  per  inch,  the  gear- 
ing to  cut  13  threads  per  inch  must  have  the  same  ratio  as  6  is  to 
13.  To  cut  16  threads  the  ratio  would  be  6  to  16. 

It  is  not  necessary  to  figure  the  size  of  gears  for  the  different 


14  ELEMENTARY     LATHE     PRACTICE. 

threads  as  all  lathes  are  provided  with  an  index  plate  that  desig- 
nates the  proper  size  gears  to  be  placed  on  the  stud  B  and  screw 
C,  Fig.  17,  for  the  desired  thread. 

To  Set  Change  Gear. — To  change  these  gears,  first  loosen  the 
nuts  holding  the  stud  and  screw  gears  B  and  C.  Next  loosen  the 
nut  G.  This  will  allow  the  intermediate  gear  to  drop  away  from 
the  stud  gear  B.  Then  loosen  the  nut  H  so  that  the  intermediate 
gear  can  be  drawn  back  away  from  the  gear  on  the  lead  screw  C. 

When  the;- gears  are  put  together,  they  should  be  set  so  that 
there  will  be  a  little  slack,  or  lost  motion,  between  the  different 
gears.  If  they  are  set  too  close  together,  they  will  make  a  great 
deal  of  noise  when  running  and  there  is  also  danger  of  breaking 
the  teeth. 

While  all  lathes  are  not  designed  alike  the  method  of  changing 
the  gears  is  very  much  the  same  on  all  machines,  except  those  hav- 
ing the  quick  change-gear  device.  With  a  lathe  having  such  a  de- 
vice, instead  of  changing  the  gears  on  the  stud  and  screw  the  same 
result  is  obtained  by  shifting  a  combination  of  levers. 

Why  Feed  Should  Be  Disconnected. — The  mechanism  that 
controls  the  feed,  or  travel,  of  the  tool  when  cutting  threads  is 
independent  of  that  used  for  the  feed  when  doing  plain  turning. 
The  two  feeds  usually  run  at  different  speeds  so  that  if  they  are 
both  in  action  at  the  same  time  the  gears  in  the  carriage  will 
break.  For  this  reason  all  lathes  are  provided  with  some  means 
of  disconnecting  the  feed  used  for  plain  turning  when  cutting 
threads. 

To  disconnect  the  feed  on  the  lathe  shown  in  Fig.  17,  move  the 
lever  J  to  the  central,  or  neutral,  position.  This  should  always 
be  done  before  starting  to  cut  the  threads. 

Speed  of  Lathe. — The  lathe  should  run  slower  for  cutting 
threads  than  for  plain  turning.  With  most  lathes  if  the  belt  is 
on  the  largest  step  of  the  cone  it  will  give  about  the  right  speed 
for  cutting  the  threads  in  this  exercise. 

The  object  of  running  the  lathe  slow  is  to  give  the  operator 
time  to  draw  back  the  tool  at  the  end  of  the  cut  and  to  obtain  a 
smoother  cut.  If  the  speed  of  the  lathe  is  too  fast,  the  cutting 
action  will  be  so  quick  that  the  tool,  instead  of  cutting  clean  and 
smooth,  will  tear  out  the  metal  leaving  a  rough  surface. 

The  slower  the  lathe  runs  the  easier  it  is  to  cut  the  threads, 
but  it  will  also  take  longer  to  do  the  job.  It  therefore  requires 


ELEMENTARY     LATHE     PRACTICE.  15 

practical  experience  to  determine  the  proper  speed  to  be  used  for 
cutting  the  different  size  threads. 

Chamfering". — After  the  lathe  and  tool  are  properly  set,  cham- 
fer off  the  sharp  corners  where  the  threads  begin  and  end  with 
the  side  of  the  thread  tool.  The  depth  of  this  cut  should  be  about 
the  same  as  that  of  the  threads  when  finished.  If  the  corners  are 
not  chamfered,  the  threads,  when  cut,  will  form  a  very  thai  edge, 
or  fin,  at  the  ends. 


of  Adjustable  Stop. — To  regulate  the  depth  of  each  cut 
an  adjustable  stop  is  used  as  shown  at  K.  First  move  the  tool  so 
that  the  point  just  touches  the  work,  then  adjust  the  screw  on 
the  attachment  K  so  that  the  cross-rest  will  not  go  in  any  farther. 
Now  move  the  carriage  by  hand  until  the  point  of  the  tool  is  a 
little  past  the  tail-stock  end  of  the  work ;  close  the  split  nut  on 
the  lead  screw  with  the  lever  E ;  and  turn  the  screw  on  the  at- 
tachment K  so  that  the  tool  can  be  moved  in  just  enough  to  take 
a  very  light  cut. 

Start  the  lathe  and  when  the  tool  has  reached  the  end  of  the 
cut  back  it  out  and  reverse  the  lathe.  By  reversing  the  lathe  the 
tool  is  returned  to  the  starting  po.nt  without  disconnecting  any 
of  the  gearing.  The  object  of  drawing  the  tool  back  is  to  prevent 
it  from  dragging  on  the  work  during  its  return. 

The  tool  will  never  travel  over  the  same  path  on  the  reverse 
as  on  the  forward  movement  of  the  lathe  on  account  of  the  slack, 
or  lost  motion,  in  the  gears. 

This  first  cut  is  taken  to  prove  that  the  lathe  is  properly 
geared,  so  the  wrork  should  be  measured  with  a  rule,  or  screw 
p^tch  gauge. 

Adjust  the  screw  at  K  until  the  tool  can  be  moved  in  deeper 
for  the  next  cut  and  repeat  the  operation  until  the  thread  is 
nearly  finished.  Then  the  tool  should  be  reset  so  that  it  will  cut 
on  only  one  side  at  a  time. 

Finishing  Side  of  Thread. — When  roughing  out  the  threads, 
the  tool  cuts  on  both  sides  of  the  po.nt  since  it  is  fed  straight  into 
the  work.  It  is  much  easier,  though,  to  finish  the  threads  smooth 
if  the  tool  cuts  on  one  side  only.  This  is  done  by  rapping  the  end 
of  the  tool  holder  so  that  it  is  turned  in  the  tool  post  just  enough 
to  change  the  position  of  the  point  of  the  tool  about  .01,  or  .02  of 
an  inch. 

To  prove  that  the  tool  is  set  over  the  proper  amount,  turn  the 


ELEMENTARY     LATHE     PRACTICE. 

|«»w , 




»rw«u'd  by  hand  a  tV\v  rw 


lathe  forward  by  hand  a  few  revolutions,  to  take  out  all  the  slack, 
or  lost,  motion  in  the  gears,  then  move  the  tool  into  the  groove  of 
the  thread  until  one  side  just  touches  the  side  of  the  thread.  The 
other  side  of  the  tool  should  then  be  about  .01,  or  .02  of  an  inch 
away  from  the  side  of  the  thread. 

After  the  tool  is  properly  adjusted,  set  the  stop  K.  The  tool 
is  then  drawn  back  and  the  lathe  reversed  until  the  tool  is  at  the 
end  of  the  work  ready  for  a  cut.  Tt  usually  requires  several  fin- 
ishing cuts  to  take  out  all  the  rough  marks  left  by  the  roughing 
cuts. 

When  this  side  of  the  thread  is  finished,  the  other  side  is  fin- 
ished in  the  sanfe' manner. 

If  the  lathe^  provided  with  a  compound  .  rest,  a  somewhat  f 
different  procedure  is  usually  followed  since  the  rest  can  be  set; 
at  an  angle  of  30  degrees  with  the  work,  as  in  Pig.  18. 

In  this  case  the  tool  is  moved  in  by  turning  the  small  hand- 
crank  M  until  the  side  at  0  hag,  been  cut  to  the  proper  depth. 
While  making  these  first  cuts,  the  stop  K  is  merely  used  to  bring 
the  cross-rest  to  the  same  p^^oj^each  time.  The  tool  is  then  ^ 
drawn  back  slightly  with  the  hand-crank  M  and r the  stop  K  ad- 
justed so  that  the  to$r  can  be  moved  straight  in  by  means 
hand-crank  Q.  This  will  finish  the  other  side  of  the  thread  at  P. 

To  determine  when  the  thr-ead  is  cut  to  the  proper  size  the 
work  is  removed  from  the.  lat^e  and  tested  with  a  standard  nut  j 
having  IT.  S.  S.  threads. 

After  the  threads  are  cut  on  this  end  of  the*  exercise,  -it  is  re 

*  \* 

versed  in  the  lathe  and  the  other  end  threaded  in  a  similar  man- 
ner. 

To  prevent  the  screw  of  the  dog  from  marring  the  portion 
already  threaded  two  nuts  should  be  screwed  on  and  the  dog  fast- 
ened to  the  nuts. 

How  to  Reset  the  Tool. — When  cutting  threads  of  this  size  and 
larger,  the  tool  usually  becomes  dull  from  taking  the  heavy  rough- 
ing cuts.  It  is  then  necessary  to  resharpen  it  before  taking  the 
fine  finishing  cuts. 

To  reset  the  tool  in  the  lathe  first  get  the  angles  correct,  as 
shown  in  Fig.  16.  Then  revolve  the  lathe  forward  by  hand  to 
take  up  the  slack  in  the  gears  and  move  the  tool  in  close  to  the 
threads.  If  the  tool  is  in  a  position  so  that  it  will  cut  too  much 
off  one  side  of  the  thre^l^it  may  be  changed  by  disengaging  the 
reversing  gears  with  the  liver  R  and  turning  the  lathe  by  hand. 


ELEMENTARY     LATHE     PRACTICE. 


17 


When  the  tool  is  in  the  proper  position  relative  to  the  groove  of 
the  thread,  the  reverse  gear  lever  R  is  reset. 

In  a  case  where  the  tool  is  off  the  desired  position  only  a  very 
little,  it  may  be  corrected  by  the  rapping  process. 

If  the  lathe  has  a  compound  rest  the  tool  may  be  brought  to 
the  correct  position  by  turning  the  hand-crank  M. 

It  would  be  well  for  beginners  to  practice  thread  cutting  on  a 
piece  of  scrap  steel  before  trying  to  cut  them  on  the  exercise. 

EXERCISE  No.  3. 
CAST  IRON  FINISHED  ALL  OVER. 


Sequence  of  Operations : 

1.  Finish  the  inside  of  Piece  A. 

2.  Drill  and  Ream  the  hole  in  Piece  B. 

3.  Mount  B  on  mandrel  and  finish  outside. 

4.  Screw  A  on  B  and  finish  the  outside  of  A. 

Piece  A. 

10  Thrds  per  1"    U.S.S. 


—2* -JM-i 

Fig.  19 
Rough  Casting 


Fig  20 
Finished  Casting 


18 


ELEMENTARY     LATHE     PRACTICE. 


USE  OF  4-JAW  CHUCK. 

To  machine  the  inside  of  piece  A  it  is  necessary  to  hold  it  in 
the  lathe  by  means  of  an  independent  four- jaw  chuck,  as  shown 
in  Fig.  21.  Work  of  this  kind  is  usually  chucked  so  that  the  out- 


side surfaces  will  be  within  1/32  of  an  inch  of  running  true. 
The  process  of  chucking  the  work  is  as  follows : 

Centering  Work  in  the  Chuck. — Place  the  work  in  the  chuck 
and  adjust  the  jaws  until  they  are  all  at  approximately  equal 
distances  from  the  circles  on  the  face  of  the  chuck.  Then  put  a 
cutting-off  tool  loosely  in  the  tool  post  and  move  it  close  to  the 
work  and  as  near  as  possible  to  the  end  of  the  chuck  jaws.  Re- 
volve the  lathe  by  hand  to  prove  if  the  work  is  centered.  If  it  is 
not  centered  to  within  1/32  of  an  inch,  readjust  the  jaws  until  it 
is.  Now  move  the  cutting-off  tool  to  the  end  of  the  work  and 
turn  the  lathe  by  hand.  If  the  end  runs  out  of  true,  rap  it  with  a 
hammer  at  such  po.nts  as  will  correct  its  position. 

Advantage  of  Proper  Chucking. — Fig.  21  shows  the  work  held 
by  the  middle  step  of  the  cone.  One  reason  for  holding  it  in  this 
way  is  to  permit  the  rough  turning  of  the  larger  step  while  in 
the  chuck.  If  the  work  were  held  by  the  small  end,  it  would  be 
apt  to  work  loose  when  taking  the  heavy  roughing  cuts  on  account 
of  the  distance  that  the  work  projects  out  and  the  small  diameter 
on  which  the  chuck  grips  compared  with  that  of  the  large  end 
which  is  to  be  turned. 

ROUGH  TURNING  AND  BORING. 

After  the  work  has  been  properly  chucked,  rough  turn  the 
end  and  the  largest  diameter  to  within  1/32  of  an  inch  of  the  fin- 
ished size. 

All  cast  iron  has  a  hard  surface,  or  scale,  from  1/64  to  1/32 
of  an  inch  deep  so  that  it  is  necessary  to  run  the  lathe  slower 
for  the  first  cut  than  for  those  made  after  the  scale  has  been  re- 


ELEMENTARY     LATHE     PRACTICE.  19 

moved.     In  taking     this  first  cut  the     tool  should  be  set     deep 
enough  to  permit  the  point  to  cut  under  the  scale. 

Speed  of  Lathe. — The  speed  of  the  lathe  in  taking  the  rough- 
ing cut  on  work  of  this  size  should  be  about  right  if  the  belt  is  on 
the  smallest  step  of  the  cone  and  the  back  gears  are  used.  After 
the  scale  is  removed,  the  lathe  may  be  run  faster. 

A  beginner  will  require  experience  before  being  able  to  de- 
termine the  proper  speeds  and  feeds  for  the  diffrent  kinds  of 
lathe  work. 

Advantage  of  Roughing  Inside. — As  the  inside  of  piece  A  must 
fit  the  outside  of  the  piece  B,  the  1 1/8  inch  hole,  the  threads, 
and  the  taper  must  be  machine  true  with  each  other,  or  else  A  will 
not  fit  into  B  properly.  Now  if  the  taper  should  be  finished  and 
the  work  moved  in  the  chuck  before  the  threads  and  the  1  1/8 
inch  hole  are  finished,  they  would  not  be  true  with  each  other. 
For  this  reason  it  would  be  well  to  rough  bore  the  inside  to  within 
1/32  of  an  inch  of  the  finished  size  before  any  of  these  three  parts 
are  finished. 

Roughing  Inside. — To  rough  bore  the  taper  use  a  regular  turn- 
ing tool.  Set  the  compound  rest  to  the  correct  angle  and  feed  the 
tool  in  at  that  angle. 

If  the  lathe  is  not  provided  with  a  compound  rest,  the  taper 
may  be  rough  bored  by  turning  both  feeds  by  hand  and  following 
the  cored  surface  as  closely  as  possible. 

The  cored  hoie  in  the  rough  casting,  Fig.  19,  is  15/16  of  an 
inch  in  diameter  which  allows  3/16  of  an  inch  for  finishing  the 
1  1/8  inch  hole  and  5/16  for  the  portion  where  the  threads  are  to 
be  cut. 

Use  of  Flat  Drill.— To  rough  bore  the  hole  a  1  1/16  flat,  or 
lathe,  drill  is  used  as  shown  in  Fig.  21.  The  holder  A  is  clamped 
in  the  tool  post  so  that  the  slot  in  it  will  hold  the  drill  at  the  cen- 
ter of  the  lathe.  If  the  drill  is  held  above  or  below  the  center,  the 
hole  will  be  drilled  larger  than  the  drill.  To  prove  that  the  slot 
in  the  holder  is  at  the  center,  move  it  close  to  the  tail-stock  center. 
After  the  holder  is  properly  set,  move  it  as  close  to  the  work  as 
possible  and  feed  the  drill  into  the  exercise  by  turning  the  hand 
crank  on  the  tail-stock. 

This  drill  removes  the  hard  surface,  or  scale,  and  also  trues 
up,  or  centers,  the  hole  to  within  1/64,  or  1/32  of  an  inch.     Now 
enlarge   the   portion  of  the  hole  where  the  threads  are   to  be  cut 
with  a  1  3/16  drill. 
I 


20 


ELEMENTARY     LATHE     PRACTICE. 


To  determine  when  this  drill  has  been  fed  in  far  enough,  mark 
on  the  drill  with  a  piece  of  chalk  the  distance  from  the  end  of  the 
work  to  the  point  where  the  recess  is  to  be  cut.  By  sighting 
across  the  end  of  the  work  the  operator  can  then  see  when  the 
drill  has  been  fed  in  the  proper  distance. 

Use  of  Boring  Bar. — To  cut  the  square  shoulder  where  the 
threads  begin  and  the  recess  where  they  end,  use  a  tool  and  boring 
bar,  as  shown  in  Fig.  22,  held  in  the  tool  post.  The  width  of  this 


Fig.  22 


u 


tool  is  5/32  of  an  inch  so  that  it  will  be  necessary  to  take  two  cuts 
to  make  the  recess  w.de  enough.  Such  a  narrow  tool  is  used  be- 
cause it  is  less  liable  to  chatter. 

This  tool  is  ground  with  clearance  at  the  sides  as  well  as  at 
the  front  and  it  should  also  be  noticed  that  it  is  wider  at  the  cut- 
ting edge  than  back  close  to  the  boring  bar.  This  is  done  so  that 
when  the  tool  is  fed  into  the  work  there  will  be  little,  or  no  chance 
of  its  binding  on  the  side. 

To  obtain  the  correct  setting  for  the  tool,  move  the  boring  bar 
into  the  hole  and  bring  it  up  close  to  one  side.  The  tool  should 
then  be  adjusted  until  its  cutting  edge  is  parallel  to  the  elements 
of  this  surface. 

The  work  is  now  all  roughed  out  so  that  it  makes  very  little 
difference  which  of  the  three  fitting  parts  is  finished  first. 

FINISHING  INSIDE 

The  1  1/8  inch  hole  has  been  drilled  with  a  1 1/16  inch  lathe 
drill,  but  as  such  a  tool  cannot  be  relied  upon  to  drill  true  to  cen- 
ter, or  size,  it  is  necessary  to  turn  it  out  with  a  boring  tool.  With 


ELEMENTARY    LATHE    PRACTICE. 


21 


this  tool  the  hole  can  be  bored  true  to  center  and  within  .01  of  an 
inch  of  the  finished  size. 

The  boring  bar  used  in  this  case  is  the  same  as  shown  in  Fig. 
22,  but  the  cutter  has  a  rounded  point  and  is  similar  to  the  tool 
used  for  outside  turning  except  that  it  is  ground  with  less  clear- 
ance. 

To  insure  accuracy  and  conserve  time,  the  hole  is  then  finished 
with  a  shell  reamer  held  in  the  lathe  as  shown  in  Fig.  23. 


Reaming1  the  Hole. — Before  starting  the  reamer,  the  hole 
should  be  bored  at  the  end,  for  a  distance  of  about  1/8  of  an  inch, 
to  the  size  which  will  just  permit  the  reamer  to  enter.  This  dia- 
meter must  be  calipered  very  carefully  and  should  be  tested  with 
the  reamer  itself.  The  rest  of  the  hole  is  then  bored  about  .01  of 
an  inch  smaller  in  diameter  to  allow  enough  material  for  finish- 
ing with  the  reamer.  Since  the  reamer  used  in  this  case  cuts  on 
the  sides  as  well  as  on  the  end,  the  hole  must  be  bored  true  to  cen- 
ter in  order  to  be  reamed  true. 

If  the  reamer  has  a  tapered  shank,  it  is  held  in  the  lathe  by  a 
square  shank  socket  and  wrench,  as  shown  in  Fig.  23,  and  is  fed 
into  the  work  by  turning  the  hand-crank  on  the  tail-stock. 

In  case  the  reamer  has  a  straight  shank,  it  is  held  as  shown  in 
Fig.  24.  Here  a  dog  is  fastened  to  the  end  of  the  reamer  and  pre- 


vented from  turning  by  a  tool  clamped  at  an  angle  in  the  tool- 
post.  The  end  of  the  tool  presses  against  the  dog  near  the  shank 
of  the  reamer  so  that  as  the  reamer  is  fed  into  the  work  the  car- 
riage of  the  lathe  is  forced  along  with  it.  This  causes  the  tool 


22  ELEMENTARY     LATHE     PRACTICE. 

to  hold  the  end  of  the  reamer  against  the  center  of  the  tail-stock. 
When  reaming  v.  ork  in  a  lathe,  if  the  tail-stock  is  off  center 
the  hole  will  be  reamed  too  large  at  the  front  end. 

Accurate  Boring*  with  Boring  Bar. — In  turning  out  holes  with 
a  boring  bar,  if  all  the  cuts  are  started  from  one  end,  that  end  will 
be  bored  larger  than  the  other.  In  case  the  hole  is  to  be  reamed, 
the  reamer  will  correct  this,  but  if  the  hole  is  to  be  finished  with 
the  boring  bar  it  will  be  necessary  to  bore  the  hole  from  both  ends. 
Th  s  is  done  by  reversing  the  feed  of  the  carriage. 

Speed  of  Lathe. — The  speed  of  the  lathe  for  reaming  should  be 
slower  than  when  using  the  boring  bar.  If  the  belt  is  on  the  sec- 
ond smallest  step  of  the  cone  with  the  back  gears  in,  the  lathe 
should  ha\e  about  the  right  speed  for  reaming.  When  using  the 
boring  bar,  the  belt  should  be  on  the  largest  step  of  the  cone  with- 
out the  back  gear. 

INSIDE  THREADING 

The  inside  threads  are  cut  in  very  much  the  same  manner  as 
the  outside  ones.  The  cutting  tool  is  held  In  the  boring  bar  and, 
like  all  boring  tools,  is  ground  with  less  clearance  than  tools  used 
for  outside  work. 

To  regulate  the  depth  of  each  cut,  the  screw  in  the  adjustable 
stop  is  placed  between  the  stop  and  the  cross-rest.  Then  by  turn- 
ing the  screw  in  after  a  cut  has  been  taken  the  cross-rest  can  be 
drawrn  back  to  permit  a  deeper  cut  with  the  tool. 

Cause  of  Threads  Breaking. — When  cutting  threads  in  cast 
iron,  they  will  break  if  the  roughing  cuts  are  too  heavy  and  are 
liable  to  if  they  are  cut  to  a  sharp  point.  Another  cause  for  the 
breaking  of  cast  iron  threads  is  the  use  of  a  dull  tool,  or  one  with 
too  little  clearance. 

Finishing1  Threads. — As  a  general  rule  cast  iron  is  machined 
without  using  a  lubricant,  but  in  finishing  threads  a  little  lard  oil 
will  aid  in  producing  a  smooth  finish. 

FINISHING  ENDS 

The  end  of  the  work  may  be  finished  by  taking  a  very  light 
cut  with  the  turning  tool  and  then  scraping  it  with  a  lathe  scrap- 


ELEMENTARY     LATHE    PRACTICE. 


23 


er,  as  shown  in  Fig.  25.    To  provide  a  rest  for  the  scraper  a  tool 


is  clamped  in  the  tool-post  and  as  close  as  possible  to  the  surface 
being  scraped. 

A  scraper  is  usually  made  from  an  old  file  ground  smooth  on 
the  two  sides  and  with  a  little  clearance  at  the  end. 


FINISHING  TAPER 


To  finish  the  taper,  set  the  compound  rest  at  an  angle  of  30 
degrees  with  the  axis  of  the  lathe.  Such  a  rest  is  normally 'at 
right  angles  with  the  lathe  axis  so  that  it  must  be  turned  through 
60  degrees  to  cut  the  30  degree  angle.  A  regular  turning  tool 
may  be  used  to  finish  this  angle,  but  it  should  be  set  so  that  the 
straight  side  will  be  nearly  parallel  with  the  tapered  surface. 

If  the  lathe  is  not  provided  with  a  compound  rest,  the  angle 
may  be  cut  with  the  side  of  a  tool  set  at  the  proper  angle.  To  set 
this  tool,  use  the  thread  and  center  gauge,  as  shown  in  Fig.  26. 

In  case  the  angle  is  any  other  than  30,  or  60  degrees,  it  is 
necessary  to  set  the  tool  with  a  bevel  and  bevel  protractor. 

After  the  taper  has  been  cut,  it  may  be  finished  smooth  by 
scraping  with  a  lathe  scraper  in  very  much  the  same  manner  as 
shown  in  Pig.  25.  The  tool  that  is  used  as  a  rest  is  set  in  as  close' 
as  possible  to  the  taper.  If  this  rest  is  too  far  away  from  the  sur- 
face being  finished,  the  scraper  will  chatter  leaving  a  rough  sur- 
face. 


24 


ELEMENTARY     LATHE     PRACTICE. 


Piece  B. 

**         10  Thrds   pe 


rj 


•f-H-l" 
Rough  Casting  Fig.  27  Finished  Casting 

DRILLING  AND  REAMING. 

This  piece  is  f  rst  placed  in  the  chuck,    as  shown  in   Fig.  28, 
ind  the  end  rough  turned  to  see  if  it  is  a  good  casting.    The  hole 


is  then  drilled  with  a  23/32  inch  twist  drill    and  reamed  out    to  ' 
size  with  a  3/4  inch  rose  reamer. 

Centering  Twist  Drill. — This  drill  will  not  bore  a  hole  in  the 
center  unless  the  point  is  controlled  in  some  way.     To  do  this,  a 
cutting-off  tool  is  clamped  in  the  tool-post   with    its   point    well/ 
above  the  center  of  the  lathe  and  is  then  moved  close  to  the  point'; 
of  the  drill.     As  the  drill  starts  to  cut,  it  wabbles  a  Little  on  ac-  2 
count  of  the  po.nt  being  off  center.     The  cutting-off  tool  is  then  •,, 
gradually  brought  against  the  drill  which  is  at  the  same  time  be-/ 
ing  slowly  fed  into  the  work  by  turning  the  hand  crank  on  the  . 
tail-stock.    It  is  necessary  to  have  the  drill  centered  true  before  it 
begins  to  cut  the  full  diameter. 

The  drill  should  <be  placed  in  the  tail-stock  so  that  the  cutting 
edges  are  vertical.  If  they  are  horizontal,  it  will  be  difficult  to 
make  the  drill  center/" 

If  the  hole  in  this  piece  were  larger,  it  would  be  cast  with  a 
core  and  then  machined  in  the  same  manner  as  the  1  I/Pinch  hole 
in  piece  A,  but  since  it  is  cast  solid,  the  hole  can  be  machined 
more  advantage&usly  by  using  a  twist  drill  and  a  rose  reamer. 

Reaming. — After   the   hole   has   been    drilled   with  the  23/32 


ELEMENTARY    LATHE    PRACTICE. 


25 


''dr  JI-,  Jbpre  it  out  with  a  small  boring  tool  for  about  1/8  of  an  inch 
from;  the  end  to  the  diameter  that  will  just  fit  over  the  reamer 
iand  insure  its  starting  true.  Ream  the  hole  with  the  reamer  held 
in  the  same  manner  as  the  twist  drill  in  Fig.  28. 

Speed  of  Lathe. — The  lathe  should  run  slower  for  reaming 
than  for  drilling.  The  speed  will  be  about  right  for  this  size 
Y earner  if  the  belt  is  on  the  largest  step  of  the  cone  without  the 
back  gears  being  used.  The  speed  for  the  drill  may  be  much 
xfaster.  With  a  high-speed  steel  drill,  the  belt  can  be  run  on  the 
second  smallest  step  of  the  cone.  If  the  drill  is  made  of  carbon 

steel,  a  slower  speed  shoul.d  be  used. 

•  u 

Advantage  of  Rose  Reamer. — In  drilling  long  holes  like  this, 
;he  drill  is  very  apt  to  get  off  center  a  little  'as  it  is  fed  deeper  into 
the  work,  even  though  it  may  have  been  started  dead  true. 

The  reamer  used  in  this  case  is  called  a  rose  reamer,  or  rose 
bit.  and  cuts  on  the  end  only.  For  this  reason,  if  the  hole  is  ap- 
proximately true,  say  withm  1/64  of  an  inch,  it  will  ream  the  hole 
straight  and  true  to  size  if  it  is  once  started  true. 

FINISHING  CORNER 

After  the  hole  is  bored  and  reamed,  the  work  may  be  finished 

;at  the  end  by  using  a  tool  ground  like  a  threading  tool,  but  hav- 

l;Shg  an  angle  at  the  point  a  little  less  than  90  degrees,  as  in  Fig. 

m 


Fig.  29 


The  boss,  or  hub,  which  is  1  3/8  inches  in  diameter,  is  finished 
with  one  cutting  edge  of  this  tool  set  nearly  parallel  to  the  work, 
vthe  point  being  a  trifle  deeper  than  the  rest.  This  will  insure  the 
full  depth  of  cut  for  the  entire  length  and  also  a  good  sharp  cor- 
ner. The  direction  of  feed  for  this  tool  should  be  from  the  end 
•and  towards  the  square  corner  or  shoulder.  If  it  is  fed  in  the  op- 
posite direction  the  tool  is  apt  to  chatter. 

This  tool  is  also  used  to  finish  the  end,  but  it  is  turned  a  little 


26 


ELEMENTARY     LATHE     PRACTICE. 


in  the  tool-post  so  that  the  other  cutting  edge  is  nearly  parallel 
to  the  surface  to  be  cut.  After  using  this  tool,  the  work  may  be 
finished  smoother  by  scraping  the  ends,  as  in  Fig.  25,  and  by  filing 
the  boss,  or  hub. 

USE  OF  MANDREL,  OR  ARBOR 

Before  this  piece  can  be  finished  on  the  outside,  it  must  be 
forced  on  a  mandrel,  or  arbor,  and  placed  in  the  lathe,  as  shown 
in  Fig.  30.  Most  commercial  shops  are  provided  with  hardened 


Fig.  30 


V 


steel  mandrels  for  this  purpose,  but  if  one  is  not  available  it  can 
be  made  from  soft  steel  in  the  following  manner: 

Making  Mandrel. — Cut  off  a  piece  of  steel  of  suitable  length, 
say  6  inches,  and  rough  turn  it  to  within  1/32  of  an  inch  of  the 
diameter  of  the  hole.  Then  turn  it  at  the  end  for  a  distance  of 
about  1/8  of  an  inch  to  the  size  that  will  just  fit  the  hole.  The 
rest  of  the  distance  is  now  turned  .002,  or  .003  of  an  inch  larger 
and  filed  for  about  3  inches  until  it  will  just  fit  the  hole.  The 
next  2  inches  are  filed  with  a  slight  taper  so  that  when  the  man- 
drel is  pressed  into  the  hole  it  will  fit  tight  enough  to  hold  the 
casting  while  't  is  being  turned.  This  kind  of  a  fit  is  called  a 
forced,  or  driving  fit. 

When  making  such  a  mandrel,  it  is  not  necessary  to  turn  that 
portion  to  which  the  dog  is  fastened. 

Mounting1  Work  on  Mandrel. — Before  pressing  the  mandrel  in, 
it  should  be  oiled  to  prevent  it  from  being  marred,  or  scored.^ 
Mandrels  are  usually  forced  in  with  a  mandrel  press,  but  if  one 
is  not  available,  they  may  be  driven  in  with  a  hammer.  When 
this  method  is  used,  a  piece  of  lead,  or  some  other  soft  material, 
must  be  held  on  the  end  of  the  mandrel  to  keep  the  hammer  from 
marring  the  center. 

FINISHING  OUTSIDE  OF  PIECE  B  TO  FIT  A 


This  casting  is  rough  turned  to  within  1/32  of  an  inch  of  the 
finished  size  before  any  part  of  it  is  finished  The  1  1/8  inch  end 
is  then  turned  until  it  fits  the  corresponding  part  of  the  hole  in 


ELEMENTARY    LATHE    PRACTICE. 


27 


piece  A  as  closely  as  possible  and  yet  not  so  tight  that  it  cannot 
be  freely  rotated.    This  kind  of  a  fit  is  called  a  close  running  fit. 

Cutting  Threads. — The  portion  to  be  threaded  should  be 
turned  a  little  smaller  than  the  diameter  at  the  bottom  of  the, 
threads  in  piece  A.  This  size  is  measured  by  means  of  the  inside 
spring-thread  calipers. 

There  is  no  recess,  or  groove,  cut  at  the  end  of  this  thread  so 
that  if  the  threading  tool  is  allowed  to  travel  farther  than  the  end 
of  the  preceding  cut.  either  the  point  of  the  tool  or  the  threads 
may  break.  To  prevent  this,  the  lathe  is  stopped  when  the  tool  is 
within  a  half  a  thread  of  the  end  and  the  cut  finished  by  turning 
the  lathe  by  hand.  Tn  this  way  the  lathe  is  kept  under  control 
and  the  tool  may  be  drawn  back  when  it  reaches  the  end  of  the 
preceding  cut.  Experienced  lathe  operators  do  not,  as  a  rule, 
turn  the  lathe  by  hand,  but  control  the  lathe  entirely  by  the 
shipper. 

The  speed  of  the  lathe  for  cutting  this  thread  will  be  about 
right  for  beginners  if  the  belt  is  on  the  second  smallest  step  of  the 
cone  and  the  back  sresrs  are  thrown  in. 

Finishing1  the  Angle,  or  Taper. — The  30  degree  angle  may  be 
cut  by  setting  the  compound  rest  to  the  correct  angle  and  using  a 
regular  turning  tool.  In  case  the  tool  leaves  a  few  tool  marks, 
they  may 'be  removed  by  f-ling. 

If  the  lathe  is  not  provided  with  a  compound  rest,  this  angle 
may  be  cut  by  sett  ng  a  square-nose  tool,  as  in  Fig.  31,  with  the 


Fig.  31 


aid  of  a  thread  gauge.      Any  other  angle  would  have  to  be  set 
with  a  bevel  and  bevel  protractor. 

This  tool  is  not  as  wide  as  the  surface  to  be  cut  because  one 
that  will  cut  the  full  width  is  very  liable  to  chatter.  It  is  there- 
fore better  to  make  several  cuts  with  a  narrow  tool.  The  surface 
can  then  be  finished  smooth  by  filing. 

The  closeness  of  the  fit  of  this  taper  with  that  in  A  can  be 


28  ELEMENTARY     LATHE     PRACTICE. 

tested  Jby  rubbing  black  paint,  which  consists  of  lamp  black  and 
oil,  on  the  tapered  surface  in  A.  When  B  is  screwed  into  A, 
marks  will  be  made  on  B  indicating  the  high  spots.  If  these  are 
not  loo  high,  they  may  be  removed  by  filing. 

FINISHING  OUTSIDE  OF  PIECE  A. 

Piece  A  may  now  be  screwed  on  B  and  the  outside  rough 
turned  to  within  1/32  of  an  inch  of  the  finished  size. 

The  ends  of  the  different  steps  are  finished  to  the  proper 
length  with  the  tool  shown  in  Fig.  29.  This  same  tool  can  then  be 
used  to  turn  the  different  diameters  to  within  0.002  or  0.003  of  an 
inch  of  the  required  size.  These  steps  are  brought  to  the  final 
size  by  filing. 

Filing. — The  file  for  this  work  should  be  less  than  1  inch  in 
width.  If  it  is  wider  than  the  steps,  a  beginner  wrill  usually  file 
the  portion  at  the  end  of  each  step  smaller  in  diameter  than  that 
which  is  close  to  the  square  corners. 

The  different  diameters  may  be  measured  accurately  with  the 
micrometer  calipers. 

KNURLING 

After  piece  A  is  finished,  it  is  removed  from  B  and  B  is  re- 
versed in  the  lathe  so  that  the  boss  may  be  knurled. 

In  case  there  is  enough  room  between  the  dog  and  the  work, 
when  held  as  in  Fig.  30,  there  is  no  need  to  reverse  the  work  for 
knurling  since  it  can  be  done  in  this  position. 

The  boss  at  the  end  of  B  is  used  as  a  handle  so  that  if  it  were 
left  smooth  it  would  be  hard  to  turn  by  hand.  The  surface  is 
therefore  made  rough  with  a  knurling  tool  as  shown  in  Fig.  32. 


Fig.  32 


The  speed  of  the  lathe  should  be  about  the  same  for  knurling 
as  for  thread  cutting.  If  the  lathe  runs  too  fast,  the  knurling  tool 
does  not  cut  satisfactorily. 

The  tool  is  set  so  that  the  face  of  the  rollers  is  parallel  with 


ELEMENTARY   LATHE    PRACTICE.  29 

the  surface  to  be  knurled.  When  starting  the  cut,  the  rollers  can 
be  forced  into  the  piece  easier  if  about  half  of  their  width  extends 
past  the  end  of  the  work. 

The  knurling  tool  should  be  pressed  into  the  work  fast  enough 
so  that  about  one  half  the  depth  of  the  finished  knurl  will  be  cut 
while  the  lathe  makes  three  or  four  revolutions.  If  the  tool  is 
forced  in  too  slow,  it  will  cut  a  finer  knurled  surface  than  the  roll- 
ers are  intended  to  cut. 

The  tool  is  fed  along  the  surface  in  the  same  manner  as  in  plain 
turning.  The  speed  at  which  the  carriage  of  the  lathe  moves  has 
no  effect  upon  the  pitch  of  the  knurled  surface  since  this  is  con-' 
trolled  by  the  pitch  of  the  grooves  in  the  rollers.  If  a  finer  knurled 
surface  is  desired,  a  knurling  tool  having  rollers  with  finer  grooves 
would  have  to  be  used. 


-^•H 


PART  II. 


VISE,  SHAPER,  DRILLING  AND  TAPPING 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


VISE  WORK 

Although  most  of  the  metal  cutting  in  the  machine  shop  can  be 
done  by  machine,  it  is  sometimes  necessary,  even  in  the  most 
modern  shops,  to  do  some  of  it  by  hand.  In  order  to  give  the 
student  practice  in  this  hand,  or  vise  work,  the  sides  A  and  B  of 
the  cast  iron  block,  Fig.  1,  are  to  be  finished  by  chipping,  filing  and 
scraping. 

EXERCISE  NO.  4 

CAST  IRON  BLOCK 

A  A 


B 


-3ft— 
Fig.  1 
Sequence  of  Operations: 

1.  Chip  and  file  side  A. 

2.  Scrape  side  A  true  to  a  surface  plate. 

3.  Chip  and  file  side  B  square  with  A. 

4.  Scrape  side  B  true  to  surface  plate. 

Chipping. — The  original  surface  of  cast  iron  is  very  hard  for  a 
depth  of  about  1/64  of  an  inch  and  is  almost  impossible  to  file.  It 
is  therefore  necessary  to  remove  this  hard  scale  with  chisels  before 
starting  to  file. 

For  this  sort  of  chipping,  cape  and  flat  chisels,  Figs.  2  and  3, 
respectively,  are  used. 


Fig.  4 


6  ELEMENTARY    MACHINE   SHOP    PRACTICE 

Parallel  grooves  are  first  cut  in  the  surface  as  shown  in  Fig.  4. 
These  grooves  must  be  just  deep  enough  to  get  under  the  scale,  i.  e., 
not  less  than  1/32"  nor  more  than  1/16"  deep.  When  they  have 
been  cut  to  within  1/4  of  an  inch  of  the  end,  the  direction  of  chip- 
ping should  be  reversed  to  prevent  breaking  out  the  cast  iron  at  the 
corner. 

The  grooves  should  be  uniformly  spaced,  in  this  case,  about  1/4" 
to  5/16"  apart.  On  heavier  work,  where  larger  chisels  are  neces- 
sary, the  grooves  are  cut  further  apart.  Generally  the  distance  be- 
tween the  grooves  should  be  about  equal  to  the  width  of  the  cape 
chisel  used. 

Care  should  be  taken  not  to  chip  one  portion  of  the  surface 
deeper  than  another ;  the  more  uniform  the  grooves  the  less  will  be 
the  filing  required  to  make  the  surface  straight. 

The  metal  ridges'  are  chipped  off  with  the  flat  chisel  shown  in 
Fig.  3. 

Sharpening  the  Chisels. — To  do  good  work  the  chisels  must  be 
kept  sharp  by  grinding  on  a  fine  grinding  wheel..  Care  should  be 
taken  not  to  hold  them  too  hard  against  the  wheel,  thus  drawing 
the  temper. 

If  the  chisels  are  to  be  used  for  very  light  cuts,  say  1/64  of  an 
inch  deep,  the  cutting  edge  may  be  ground  to  a  smaller  angle  than 
is  shown  in  Figs.  2  and  3. 

FILES  AND  FILING 

Files. — While  there  is  a  large  variety  of  shapes  and  sizes  of  files 
manufactured,"  only"  the  ones  to  be  used  on  these  exercises  will  be 
described.  Students  desiring  further  information  on  files  should 
consult  the  catalogue  of  some  standard  file  manufacturer. 

Files  are  designated  by  their  size,  type,  and  the  coarseness  or 
cut  of  their  teeth. 

The  size  refers  to  the  distance  from  the  end  of  the  file  to  the 
point  where  the  tang  begins,  Fig.  5. 

The  type  refers  to  the  general  shape  of  the  file.  Those  most 
commonly  used  in  a  machine  shop  are  the  mill,  flat,  Hand,  square, 
round  and  half-round  files. 

The  mill,  flat  and  hand  files  are  very  similar  in  shape,  but  differ 
from  one  another  in  detail. 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


Flat 


Hand 


Fig.  5. 

The  mill  file  is  uniform  in  thickness,  tapered  in  width  and  is 
single  cut,  i.  e.,  has  only  one  course  of  teeth.  It  is  used  principally 
for  lathe  work. 

The  flat  file  is  tapered  in  both  width  and  thickness  and  is  double 
cut.  It  is  intended  mainly  for  general  use  and  is  not  suitable  for 
lathe  work. 

The  hand  file  is  uniform  in  width,  tapered  in  thickness  and 
double  cut.  It  is  a  little  wider  than  the  mill  and  flat  file  and  has 
one  safe  edge,  i.  e.,  one  edge  without  teeth. 

The  advantage  of  this  safe  edge  is  that  the  file  may  be  used  close 
up  to  a  square  corner  without  cutting  in  at  the  side.  This  file  is 
preferred  by  machinists  for  flat  surfaces,  although  the  flat  file  may 
also  be  used  for  such  work.  An  edge  of  a  flat  file  may  be  made 
safe  by  grinding  off  the  teeth. 

The  common  square  file  is  tapered  and  double  cut.  It  is  used 
for  filing  square  and  rectangular  holes  and  on  square  corners.  For 
this  kind  of  work  one  edge  should  be  safe. 

The  common  round  file  is  tapered  and  double  cut.  It  is  used  for 
filing  round  holes,  concave  surfaces,  etc. 

The  half-round  file  is  tapered  and  double  cut.  It  is  used  on 
large  round  holes,  concave  surfaces  and  acute  angles.  The  latter 
use  is  illustrated  in  Fig.  31,  page  25. 

The  coarseness  or  cut  of  a  file  refers  to  the  spacing  of  the  teeth. 
The  three  different  spacings,  or  cuts,  in  common  use  are  the  bastard, 


8  ELEMENTARY    MACHINE    SHOP    PRACTICE 

second  cut  and  smooth.    Practically  all  of  the  common  files  may  be 
obtained  in  any  of  these  three  cuts. 

Filing. — Having  removed  the  scale  on  the  cast  iron  block  with 
chisels,  the  surface  should  be  filed  approximately  straight  with  a 
hand  bastard  file.  If  a  hand  file  is  not  available  a  flat  file  may  be  used. 

In  the  first  rough  filing,  a  full  stroke  of  the  file  is  used,  but  as 
the  surface  approaches  a  true  plane  this  may  be  changed  to  a  short 
stroke.  A  short  stroke  makes  it  easier  to  control  the  file.  Rock- 
ing the  file  should  be  avoided  as  it  causes  the  edges  and  corners 
of  the  work  to  be  filed  lower  than  the  center. 

To  test  the  straightness  of  the  surface  being  filed  the  edge  of  a 
steel  rule  is  held  on  it  in  several  positions. 

When  filing  work  of  this  kind  it  is  advisable  to  file  in  different 
directions,  i.  e.,  parallel  with  one  edge,  crosswise  and  diagonally. 

The  teeth  of  all  files  are  made  to  cut  on  the  forward  stroke.  For 
this  reason  the  pressure  should  be  relieved  on  the  return  or  back- 
ward stroke. 

It  will  be  noticed  upon  sighting  along  the  edge  of  a  hand  file 
that  the  thickness  does  not  taper  uniformly,  both  sides  being  slight- 
ly convex.  The  curves  are  supposed  to  be  uniform,  but  the  warping 
that  occurs  in  tempering  causes  greater  convexity  at  one  place  than 
another.  By  using  the  file  at  the  point  of  greatest  convexity  and  by 
giving  it  a  short  stroke  the  work  may  be  filed  straight  even  though 
the  file  does  rock  a  little.  If  the  file  is  warped  to  the  extent  that 
one  side  is  slightly  concave  it  will  be  impossible  to  file  the  work 
straight  with  that  side. 

After  the  surface  has  been  filed  straight  with  the  coarse  or  bast- 
ard file  it  is  finished  smoother  with  a  hand  or  flat  smooth  file.  In- 
stead of  filing  in  different  directions,  as  in  rough  filing,  the  strokes 
should  be  parallel  with  one  edge  of  the  work.  This  causes  all  the 
scratches  or  lines  made  by  the  file  to  be  parallel,  giving  the  surface  a 
better  appearance.  If  it  is  to  be  scraped,  as  in  this  case,  this  will  also 
make  it  much  easier. 

When  filing  cast  iron  the  file  dust  should  never  be  brushed  off 
the  work  with  the  hand,  as  the  hand  deposits  more  or  less  grease, 
causing  the  file  to  slip  and  dull  quickly.  Machinists  usually  blow 
off  the  dust.  When  filing  wrought  iron  or  steel,  oil  or  grease  does 
no  harm,  in  fact  oil  is  sometimes  used  to  produce  a  smooth  finish. 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


SCRAPING 

After  the  surface  A  has  been  filed  smooth  and  approximately 
straight,  it  is  finished  to  a  plane  surface  with  a  surface  plate  and 
scraper. 

Use  of  Surface  Plate. — To  locate  the  high  places  on  a  flat 
surface  a  surface  plate,  Fig.  6,  is  used.  The  size  of  the  plate  is 
usually  a  little  larger  than  the  surface  being  scraped.  The  side  A 
is  first  covered  with  a  thin  film  of  paint  made  of  lamp  black  and 
lard  oil.  It  is  then  placed  in  contact  with  the  surface  to  be  scraped 
and  moved  around  over  it,  marking  the  high  spots. 


A 
Fig.  6 

The  paint  should  be  spread  on  the  plate  with  the  finger  tips  and 
just  thick  enough  to  cover  it.  If  waste  or  cloth  is  used,  lint  is  de- 
posited on  the  plate  and  interferes  with  the  marking.  If  it  is  spread 
on  too  thick,  the  low  places  will  be  marked  as  well  as  the  high  ones. 

It  is  very  easy  to  locate  the  high  spots  if  the  work  is  a  little 
concave,  but  if  a  little  convex  the  plate  is  apt  to  rock  when  moved 
over  the  surface,  thus  marking  the  low  as  well  as  the  high  spots. 
This  makes  it  very  important  to  use  as  little  paint  on  the  surface 
plate  as  possible,  and  to  move  it  over  the  work  without  rocking. 

After  locating  the  high  spots  the  scraper  is  used  on  them  and 
the  work  again  tested  with  the  plate.  These  operations  are  re- 
peated until  the  surface  is  true. 

Use  of  the  Scraper. — In  use  the  scraper  is  held  firmly  with  both 
hands  at  about  the  angle  shown  in  Fig.  7.  The  cutting  is  done  by 


10  ELEMENTARY    MACHINE    SHOP    PRACTICE 

holding  it  down  hard  on  the  work  and  moving  it  forward  in  the 
direction  indicated  by  the  arrow.  If  the  handle  is  held  too  high  or 
too  low  the  scraper  will  not  cut  satisfactorily.  A  little  practice  will 
be  required  before  a  beginner  can  properly  control  it. 


Fig.  7 

When  using  the  scraper  it  will  be  noticed  that  it  has  a  tendency 
to  chatter,  causing  a  slightly  wavy  line  cut  instead  of  a  smooth  one. 
If  all  the  scraping  is  done  in  one  direction  these  chatter  marks  be- 
come deeper.  This  may  be  avoided  by  varying  the  direction  of  the 
scraping  a  little  after  each  marking  with  the  surface  plate. 

The  scraper  is  usually  made  from  an  old  10-inch  file  by  grinding 
off  the  teeth  and  forging  it  to  the  shape  shown  in  Fig.  8. 

Grinding  the  Scraper. — After  forging  and  hardening,  the 
scraper  is  ground  straight  on  the  side  B,  Fig.  8,  and  slightly  convex 
across  the  end  A.  If  the  latter  edge  is  curved  too  much,  the  scraper 
will  take  too  narrow  a  cut,  while  if  it  is  perfectly  straight  the  cut 
will  be  so  wide  that  it  will  not  be  smooth.  The  scraper  should  be 
ground  so  as  to  take  a  cut  about  1/4  of  an  inch  or  wider. 

The  edge  C  should  be  ground  at  right  angles  with  the  center 
line  of  the  scraper. 

Caution. — The  scraper  is  made  of  carbon  steel  and  is  tempered 
very  hard.  Beginners  are  therefore  cautioned  not  to  draw  the  tem- 
per by  grinding  it  too  fast.  This  often  happens  without  being 
noticed  so  that  the  beginner  is  unable  to  understand  why  his  scraper 
will  not  cut. 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


11 


A                     C 

B 

B 

5" 

f 

i 
1 

K  r 

.1.. 

Fig.  8 


Fig.  9 


Fig.  10 


Oilstoning  the  Scraper. — The  grinding  wheel  produces  a  some- 
what rough  cutting  edge  which  must  be  oilstoned  before  the 
scraper  will  cut  smoothly.  This  oilstoning  is  done  by  moving  the 
end  and  the  sides  of  the  scraper  alternately  over  the  surface  of  a 
flat  oilstone. 

When  oilstoning  the  end  it  may  be  held  vertically,  Fig.  9,  or  at 
a  slight  angle,  as  in  Fig.  10.  If  held  at  an  angle  the  sharpening  is 
done  a  little  quicker  and  the  edge  will  be  slightly  beveled.  Such  an 
edge  will  cause  less  chattering  than  the  one  obtained  by  oilstoning 
as  in  Fig.  9.  When  one  edge  has  been  sharpened  the  scraper  is 
turned  over  and  the  other  edge  sharpened  in  the  same  manner. 

Fig.  11  shows  the  correct  position  for  oilstoning  the  side.  The 
handle  should  not  be  raised,  as  in  Fig.  12,  as  this  would  take  off 
the  sharp  edge.  A  fine  wire  or  feather  edge  is  produced,  no  matter 
how  hard  the  scraper  is  tempered.  To  take  advantage  of  it,  the 
scraper  should  be  oilstoned  on  the  side  last  if  it  is  to  cut  on  the 


12 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


forward  stroke,  as  in  Fig.  7,  and  on  the  end  last  if  it  is  to  cut  on  the 
draw  stroke. 


Fig.  11 


Fig.  12 

In  order  to  do  good  work  the  scraper  must  be  kept  very  sharp. 
It  will  be  necessary  to  oilstone  it  several  times  while  scraping  the 
surface  of  this  exercise. 

When  the  scraper  has  been  repeatedly  oilstoned  so  that  the  cut- 
ting edges  are  worn  off,  the  end  should  be  reground  on  the  grind- 
ing wheel  to  the  original  shape,  as  shown  at  C  in  Fig.  8. 

Finishing  Side  B. — After  side  A  of  Exercise  4  has  been  finished, 
the  side  B  is  squared  with  A  by  the  same  process,  i.  e.,  by  chipping, 
filing  and  scraping. 

If  B  is  very  much  out  of  square  with  A,  one  side  of  B  may  be 
chipped  a  little  deeper  than  the  other.  In  doing  this  it  will  be  better 
to  take  several  light  cuts  with  the  cape  chisel  than  to  try  to  remove 
too  much  metal  in  one  cut.  Too  deep  a  cut  will  cause  the  edge  of 
the  chisel  to  break. 


14  ELEMENTARY    MACHINE    SHOP    PRACTICE 

SHAPER  WORK 

An  up-to-date  shaper  is  shown  in  Fig.  13.  The  four-step  cone 
drive  with  back  gears  gives  eight  speeds.  Two  sides  as  well  as  the 
top  of  the  table  are  provided  with  slots  for  clamping  work  that  is 
too  large  to  be  held  in  the  vise. 

The  table  may  be  raised  or  lowered  by  means  of  the  hand  crank 
shown  at  the  end  of  the  cross-rail.  By  placing  this  crank  on  the 
shaft  immediately  above  it  the  table  may  be  fed  horizontally  by 
hand. 

The  automatic  table  feed  is  started,  stopped  or  reversed  by 
means  of  a  small  knobbed  pin  which  engages  the  ratchet  gear  at  the 
end  of  the  cross-rail.  The  rate  of  feed  is  varied  by  changing  the 
position  of  a  large  knobbed  pin  on  the  disc  near  the  driving  cone. 
The  hand  crank  above  this  disc  is  used  for  changing  the  length  of 
the  stroke.  The  position  of  the  stroke  is  changed  by  loosening  the 
lever  on  top  of  the  ram  and  turning  the  squared  shaft  shown  near 
the  head  of  the  ram. 

Shapers  are  usually  designated  by  their  maximum  length  of 
stroke ;  as,  a  16-inch  or  a  20-inch  shaper. 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


15 


Fig.  13 
20-INCH  SHAPER 


16 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


EXERCISE  NO.  5 


PLANING   ONE   SURFACE   SQUARE   WITH   ANOTHER 

Sequence  of  Operations: 

1.  Clamp  in  shaper  vise  and  plane  side  D  square  with  A. 

2.  Plane  the  ends  E  and  F  square  with  the  sides  A,  B,  and  D. 

In  taking  up  the  exercise  on  the  shaper  it  is  assumed  that  the 
sides  A  and  B  of  the  cast  iron  block  in  Fig.  14  have  been  finished 
true  and  square  in  the  vise.  The  other  sides  are  to  be  finished  on 
the  shaper  to  the  dimensions  given. 

First  lay  off  the  width  of  the  side  C  with  a  scriber  and  combina- 
tion square,  as  shown  in  Fig.  15,  marking  a  line  2  5/8  inches  from 
the  side  B  and  parallel  with  it.  In  order  to  make  the  scriber  marks 
plainly  visible  the  surface  should  be  chalked.  This  is  especially 
necessary  when  the  hard  scale  has  not  been  removed. 


15 


Clamping  the  Work. — The  work  is  clamped  in  the  shaper  vise 

with  the  finished  side  B  resting  on  the  base  and  with  the  side  A 

against  the  stationary  jaw  of  the  vise,  as  in  Fig.  16.  A  piece  of 
paper  should  be  kept  under  each  end  of  B. 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


17 


The  clamping  bolt  J  may  be  left  loose  until  the  jaw  is  close  to 
the  work.  It  should  then  be  tightened  so  that  as  the  jaw  is  screwed 
up  against  the  work  it  will  not  be  raised  off  the  base  of  the  vise. 


D    2 


" J 


Fig.  16 


The  narrow  metal  strip  shown  at  H  should  be  about  1/16"  x 
1  /2"  x  6".  It  is  used  so  that  when  the  vise  is  tightened  the  pressure 
on  the  block  will  be  about  at  the  center.  This  holds  the  side  A  tight 
against  the  solid  jaw.  By  rapping  side  D  with  a  hammer  B  is 
forced  down  on  the  base  of  the  vise  until  the  paper  at  both  ends  is 
tight. 

The  work  is  now  ready  for  the  roughing  cut.  This  is  taken 
with  a  tool  or  bit  similar  to  the  one  used  on  the  lathe,  but  which 
has  less  clearance  since  it  cuts  along  a  straight  line.  The  lathe 
tool  holder  is  sometimes  used  on  the  shaper,  but  a  regular  shaper 
tool  holder,  Fig.  17,  is  preferred.  The  latter  has  an  adjustable 
head  or  clamp  so  that  the  tool  may  be  turned  at  different  angles. 
The  piece  of  tool  steel  used  in  such  a  holder  should  always  be  longer 
than  the  diameter  of  the  head,  otherwise  it  will  not  be  held  firmly. 

Depth  of  Cut. — The  depth  of  the  roughing  cut  depends  mainly 
upon  the  size  of  the  machine  and  the  amount  of  metal  to  be  removed. 
If  1/8  of  an  inch  is  to  be  cut  off  take  a  little  more  than  half  that 
amount  the  first  cut. 

Rate  of  Feed. — This  also  depends  largely  upon  the  size  of  the 
machine.  With  large  and  heavy  machines  deep  cuts  may  be  taken 
and  coarse  feeds  used. 


18 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


[ J 


Fig.  17 


Fig.  18 


If  a  small  shaper  is  used,  as  is  generally  the  case  with  work  of 
this  sort,  the  rate  of  feed  with  a  cut  about  1/8"  deep,  may  be  about 
1/64  of  an  inch.  With  a  cut  only  1/16"  deep  the  feed  may  be  in- 
creased to  1/32"  per  stroke. 

Testing  the  Work  for  Squareness. — After  the  first  roughing 
cut,  a  finishing  cut  is  taken  and  the  work  removed  from  the  vise. 
It  is  then  tested  with  a  square  to  make  sure  that  the  surface  being 
machined  is  square  with  side  A.  The  stationary  jaw  cannot  be  de- 
pended upon  to  hold  the  work  square. 

The  finishing  tool,  Fig.  18,  is  forged  from  a  piece  of  carbon  steel. 
Care  should  be  used  in  grinding  it  not  to  draw  the  temper.  The 
advantage  of  using  carbon  steel  instead  of  high  speed  steel  for  this 
tool  is  that  it  makes  a  smoother  finishing  cut  and  is  cheaper  and 
easier  to  forge.  The  cutting  edge  should  be  ground  as  straight  as 
possible.  It  may  be  a  little  convex  but  never  concave.  The  clear- 
ance angle  B  should  be  about  10°  or  15°. 

Setting  the  Finishing  Tool. — In  order  to  take  a  smooth  finish- 
ing cut,  the  tool  should  be  set  with  the  cutting  edge  parallel,  or 
nearly  so,  with  the  surface  to  be  planed.  This  is  done  by  clamping 
it  loosely  in  the  tool  post  and  over  but  not  touching  the  work.  If 
the  cutting  edge  is  not  parallel  with  the  work,  rap  the  tool  until  it 
appears  to  be  so.  Feed  the  tool  down  with  the  hand  crank  until  it 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


19 


just  touches  the  work.  Now  move  the  ram  of  the  shaper  forward 
by  pulling  the  belt  by  hand.  The  fine  chip  or  dust  removed  by  the 
tool  will  show  if  it  is  set  in  the  proper  position. 

Direction  of  Feed. — If  the  tool  appears  to  cut  deepest  at  the 
center,  it  may  be  fed  in  either  direction,  Fig.  19,  but  if  it  is  set  so 
that  one  side  cuts  slightly  deeper  than  the  other,  as  in  Fig.  20,  the 
direction  of  the  feed  should  be  as  indicated  by  the  arrow.  Feeding 
in  the  opposite  direction  is  apt  to  make  the  tool  chatter  because  of 
the  wide  cutting  edge  that  is  in  contact  with  the  work. 


Fig.   19 


Fig.  20 


The  curve  of  the  cutting  edge  in  Fig.  19  and  the  angle  at  which 
the  tool  is  set  in  Fig.  20  are  greatly  exaggerated.  The  cutting  edge 
should  be  straight  within  .002  or  .003  of  an  inch  and  one  side  should 
not  be  set  more  than  .002  or  .003  deeper  than  the  other. 

Depth  of  Finishing  Cut. — The  finishing  tool  is  intended  for 
shallow  cuts  of  not  more  than  .01  of  an  inch  and  works  better  if  still 
less  is  taken.  In  general  practice  it  is  customary  to  plane  to  the 
finish  line  with  a  roughing  tool  and  use  the  finishing  tool  merely  to 
remove  the  marks  of  the  roughing  tool.  If  .02  or  .03  of  an  inch 
are  to  be  removed  several  cuts  should  be  taken. 

Rate  of  Feed. — As  the  finishing  tool  has  a  wide  cutting  edge  a 
coarse  feed  may  be  used.  In  this  case  about  1/8  of  an  inch  per 
stroke  will  do.  With  most  shapers  this  is  about  equivalent  to  one- 
half  turn  of  the  hand  crank.  The  feeding  should  be  done  by  hand 
and  care  taken  to  note  the  position  of  the  crank  after  each  turn. 
This  insures  a  uniform  rate  of  feed. 

Resetting  Work. — After  the  first  finishing  cut,  the  work  is 
removed  from  the  shaper  vise  and  tested  to  see  if  the  sides  A  and 
D  are  square  with  each  other  and  if  side  D  is  parallel  with  B,  Fig. 


20 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


16.  In  case  D  is  not  square  with  A  the  setting  in  the  vise  may  be 
corrected,  within  certain  limits,  by  having  the  metal  strip  H  higher 
or  lower.  When  this  strip  is  near  the  top  of  the  vise  the  block  will 
be  very  slightly  tipped  so  that  the  edge  2  will  be  a  little  higher 
than  1.  With  H  at  or  close  to  the  bottom  the  effect  will  be  just  the 
opposite  and  a  little  more  metal  can  be  cut  off  at  edge  1  than  at  2. 

If  the  two  sides  B  and  D  are  not  parallel  additional  pieces  of 
paper  may  be  placed  under  the  thickest  end. 

It  may  be  necessary  to  take  several  trial  cuts  before  the  block 
is  properly  set  in  the  vise.  These  cuts  should  be  taken  with  the 
finishing  tool  since  it  is  quickly  fed  across  the  work  and  does  not 
remove  much  metal. 

The  work  is  now  machined  to  the  finished  size.  If  it  is  neces- 
sary to  remove  more  than  1/32  of  an  inch  of  metal,  time  will  be 
saved  by  first  using  the  roughing  tool,  as  the  finishing  tool  is  not 
intended  to  take  more  than  .01"  per  cut. 

Planing  the  End. — To  plane  the  end  of  the  block  it  is  held  in 
the  vise  .in  the  same  manner  as  when  planing  side  D.  It  is  first  set 
approximately  straight  by  using  the  square  as  in  Fig.  21.  In  this 
view  the  solid  jaw  of  the  vise  is  not  shown. 

The  base  of  the  vise  cannot  be  relied  upon  to  be  parallel  with  the 
travel  of  the  tool  so  that  a  trial  roughing  and  finishing  cut  should 
be  taken  to  test  the  squareness  of  the  surface  E  with  the  sides  B 
and  D. 


Fig.  21 

If  the  block  is  not  set  square  it  may  be  tilted  a  little  in  the  vise 
by  holding  the  grain  end  of  a  piece  of  wood  against  one  corner  and 


ELEMENTARY    MACHINE    SHOP    PRACTICE  21  f 

rapping  the  wood  with  a  hammer.    Another  trial  cut  should  then  be 
taken  and  the  process  repeated  if  it  is  not  square. 

To  Prevent  Corners  from  Breaking. — It  will  be  noticed  that 
both  the  finishing  and  roughing  tools  break  off  the  corner  of  the 
work  at  the  outer  end  of  the  cut.  To  prevent  this  the  corner  is 
filed  off  at  an  angle  of  about  20°  with  the  surface  being  planed,  and 
as  deep  as  the  finishing  cut  is  to  be. 

On  work  of  this  size  the  corner  should  be  filed  off  when  the  sur- 
face has  been  planed  to  within  1/32  or  1/16  of  an  inch  of  the  finished 
size.  The  important  thing  is  to  be  sure  to  file  off  the  corner  before 
it  breaks  out  deeper  than  the  finished  size. 


22 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


Fig.  22 

PLANING  ONE  SURFACE  PARALLEL  WITH  ANOTHER 
AND  PLANING  ANGLES 


2. 
3. 

4. 

5. 


Sequence  of  Operations: 

1.     Lay  off  on  one  end  of  block  the  outline  of  the  finished  piece. 
Clamp  in  vise,  Fig.  23. 

Plane  side  C  to  size  with  roughing  and  finishing  tools. 
Rough  out  the  angles  with  a  roughing  tool,  Figs.  24  and  25. 
Finish  the  angles. 

In  laying  off  the  outline  of  the  finished  piece  the  combination 
square  can  be  used,  as  before,  for  the  measurements  and  to  mark 
the  90°  angle.  A  thread  gauge  or  a  bevel  protractor  is  used  for  the 
60°  angle. 

Clamping  in  Vise. — The  work  is  clamped  in  the  vise  as  shown 
in  Fig.  23.  The  parallels  J  and  K  are  longer  than  the  work  and 
high  enough  so  that  the  jaws  of  the  vise  grip  on  about  1/2"  of  the 
work.  The  object  in  clamping  on  only  a  small  area  of  the  sides  is 
to  make  it  easier  to  rap  the  work  down  on 'the  parallels. 

C 


B 


.--  Fig.  23 

Clamp  the  work  tight,  and  rap  the  top  with  a  hammer  to  force 
it  down  tight  on  the  parallels. 


5 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


23 


% 


Planing  One  Side  Parallel  with  Another. — After  taking  a 
roughing  and  finishing  cut,  caliper  the  block  at  each  corner  to  see  if 
it  is  uniform  in  thickness.  If  one  corner  is  thicker  than  another, 
place  one  or  more  pieces  of  paper  under  that  corner  and  take  an- 
other trial  cut.  This  operation  is  repeated  until  the  sides  A  and  C 
are  parallel. 

Roughing  Out  the  Angles. — The  angles  are  roughed  out  with 
the  regular  roughing  tool,  cutting  as  close  to  the  lines  as  possible. 
These  roughing  cuts  should  be  heavy  so  as  to  remove  the  metal 
quickly.  The  tool  should  be  started  at  the  outside  and  fed  toward 
the  center.  If  the  automatic  feed  is  used  it  should  be  disengaged 
when  the  tool  is  within  about  1/16  of  an  inch  of  the  finish  line. 
When  roughing  out  the  angles,  set  the  head,  clapper  box  and  tool 
as  in  Figs.  24  and  25. 

Setting  the  Head,  Clapper  Box,  and  Tool. — Loosen  the  clamp- 
ing screw  N,  Fig.  24,  and  move  the  clapper  box  to  about  the  angle 
shown.  The  side  of  the  tool  should  be  nearly  vertical  as  at  0. 

Setting  the  clapper  box  at  this  angle  causes  the  tool  to  swing 
way  from  the  vertical  side  of  the  work  on  the  return  stroke  of  the 
aper.     If  it  were  set  at  the  opposite  angle  it  would  swing  into  the 
work. 


Fig.  24 


24  ELEMENTARY   MACHINE    SHOP    PRACTICE 

For  the  60°  angle  set  the  head  to  an  angle  of  30°  with  the  verti- 
cal, using  the  graduations  on  the  quadrant  of  the  head  R,  Fig.  25. 
Move  the  clapper  box  to  about  the  angle  shown.  It  should  be 
noticed  that  the  angle  at  which  this  is  set  is  just  the  opposite  of  the 
one  used  when  cutting  the  90°  angle.  This  is  because  the  tool  is 
to  cut  on  the  opposite  side. 


— R 


Fig.  25 

Finishing  the  60°  Angle. — The  tool  for  finishing  the  angle  is 
ground  a  little  less  than  60°,  and  with  cutting  edges  on  the  side  and 
bottom,  L  and  M,  Fig.  26. 

First  adjust  it  so  that  the  bottom  edge  is  nearly  parallel  with  the 
top  of  the  block  as  at  I  in  Fig.  27,  being  sure  that  the  point  is 
slightly  deeper,  say,  about  .001  of  an  inch,  than  the  rest  of  the  tool. 
To  prove  that  this  is  so,  pull  the  belt  by  hand  with  the  tool  just 
touching  the  work.  The  deepest  part  of  the  tool  will  remove  a  small 
chip  or  some  dust. 

Move  the  tool  to  the  side  of  the  angle  at  G  and  feed  it  down  with 
the  hand  crank  to  remove  the  round  corner  left  by  the  roughing 
tool.  Finish  the  bottom  by  feeding  the  tool  from  the  outer  edge 
into  the  corner.  The  point  of  the  tool  being  set  deeper  insures  the 
full  depth  of  the  cut  to  the  sharp  corner. 

Start  a  cut  from  the  top  of  the  60°  angle  and  feed  down  to  the 
bottom.  Now  adjust  the  tool  so  that  it  is  nearly  parallel  to  the 
side  as  at  H  in  Fig.  28,  being  sure  that  the  point  cuts  the  deepest. 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


25 


Take  a  finishing  cut  beginning  at  the  top  and  feeding  down  until 
the  point  just  touches  the  bottom. 


~\^U 


Fig.  26 


Fig  28 


This  tool,  like  practically  all  finishing  tools,  should  be  kept  sharp 
by  grinding  and  oilstoning.  It  should  not  be  used  for  cuts  of  more 
than  .01  of  an  inch  in  depth. 

Finishing  the  Right  Angle. — When  the  60°  angle  has  been  fin- 
ished, the  90°"~*angle  is  finished  in  about  the  same  manner.  The 
head  must  be  returned  to  its  vertical  position  and  the  clapper  box 
tilted  as  in  Fig.  24.  The  tool  used  is  ground  a  little  less  than  90°, 
Fig.  30. 

The  bottom,  or  base  of  the  angles,  S  and  T,  Fig.  30,  should  be 
finished  to  the  same  level.  To  do  this  the  tool  is  set  so  that  it  just 
touches  the  surface  T.  The  final  finishing  cut  is  then  taken  on  S 
without  changing  the  height  of  the  tool. 

Filing  the  Angles. — After  the  angles  are  machined  they  may 
be  finished  smoother  with  a  file.  A  10-inch  smooth  square  file  with 
a  safe  edge  may  be  used  for  the  right  angle  as  at  U,  Fig.  31,  and  a 
10-inch  smooth  half-round  file  for  the  60°  angle.  The  latter  should 
have  a  safe  edge  at  V  so  it  will  not  cut  into  the  side  when  filing  the 
bottom. 


X|U 


Fig.  30 


Fig.  31 


26 ELEMENTARY    MACHINE    SHOP    PRACTICE 

DRILLING  AND  TAPPING 

The  size  of  a  drill  press  is  determined  by  the  maximum  diam. 
of  the  work  which  can  be  centered  with  the  spindle.  Hence  on  a 
16-inch  machine  the  distance  from  the  center  line  of  the  spindle  to 
the  column  is  about  8  inches. 

A  16-inch  drill  press  is  shown  in  Fig.  32.  With  a  five-step  cone 
it  has  five  spindle  speeds,  ranging  from  150  to  1700  revolutions  per 
minute.  This  makes  it  an  excellent  machine  for  light  drilling. 
Drills  larger  than  1/2  inch  are  not  generally  used.  The  spindle 
feed  is  controlled  by  the  hand  lever  at  the  side  of  the  spindle.  The 
table  may  be  raised  or  lowered  by  means  of  the  hand  crank  on  the 
column. 

Fig.  33  shows  a  20-inch  complete  drill  with  back  gears.  It  has 
8  changes  of  speed,  ranging  from  25  to  300  revolutions  per  minute. 
The  back  gears  are  located  at  the  top  of  the  machine  and  are  shifted 
by  means  of  the  lever  shown  directly  beneath  them.  This  machine 
has  both  hand  and  automatic  feeds  and  is  also  provided  with  an 
automatic  stop  for  drilling  a  number  of  holes  of  the  same  depth. 
The  drills  used  generally  range  from  1/4  inch  to  1  1/2  inches,  but 
larger  or  smaller  ones  can  be  used. 

When  work  is  clamped  to  the  table  of  the  machine,  it  may  be 
moved  to  any  desired  position  for  drilling  by  rotating  the  table  and 
swinging  the  table  arm  about  the  column.  To  hold  the  table  in 
position  the  wrench  shown  underneath  it  and  a  similar  one  on  the 
column  are  tightened. 

The  Hi-Speed  Drill  Press  shown  in  Fig.  34  is  built  a  little  larger 
and  heavier  than  the  one  just  described.  This  machine  will  drive 
drills  of  high  speed  steel  up  to  1  1/4  inches  in  diameter  to  their  full 
capacity.  Eight  changes  of  speed  from  90  to  610  revolutions  per 
minute  are  obtained  by  means  of  the  enclosed  gears  at  the  top  of 
the  machine.  It  is  also  provided  with  hand  and  automatic  feeds 
and  an  automatic  stop. 


ELEMENTARY    MACHINE    SHOP    PRACTICE  27 


Fig.  32 
16-INCH  DRILL  PRESS 


28 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


Fig.  33 
20-INCH  COMPLETE  DRILL 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


29 


Fig.  34 
HI-SPEED  DRILL  PRESS 


30 


ELEMENTARY   MACHINE    SHOP    PRACTICE 


EXERCISE  NO.  7 

Piece  A  is  an  unfinished  cast  iron  plate. 
Piece  B  is  Exercise  No.  6. 


'  L.U       'A   j  J..i 

jp£l| 

B   P| 

6 

\          C 

I 

V 

1 

K 

L 

M 

N 

^ 

H 

D 

J 

Fig.  35 


Fig.  36 


Sequence  of  Operations  : 

1.     Grind  the  rough  surfaces  of  piece  A. 
Lay  off  the  centers  for  holes  in  piece  A. 
Drill  1/2  inch  holes  in  piece  A. 
Place  A  on  B  and  scribe  position  of  holes  on  B. 
Drill  B  with  13/32"  drill  13/16"  deep. 
Tap  holes  in  B  with  1/2-inch  U.  S.  S.  plug  tap. 
Tap  bottom  of  holes  with  1/2-inch  U.  S.  S.  bottom  tap. 
If  screws  bind  in  holes  of  piece  A  file  with  round  file. 


2. 

3. 
4. 

5. 
6. 
7. 
8. 


Grinding  Piece  A.  —  As  it  comes  from  the  foundry  the  cast  iron 
piece  A  is  usually  rough.  It  should  be  smoothed  up  on  the  grinding 
wheel  before  laying  out  the  holes. 

Laying  Out  the  Centers  of  the  Holes.  —  Piece  A  being  a  rough 
and  unfinished  casting  is  not  apt  to  be  square  or  true  to  size.  It  is 
therefore  advisable  to  first  mark  the  center  lines  CD  and  EF, 
Fig.  36. 

To  do  this  the  surface  is  first  chalked  to  make  the  lines  plainly 
visible.  Mark  C  and  D  at  the  center  of  the  two  ends  and  as  close  to 
the  ends  as  possible.  Center  punch  them  with  a  small  center  punch 
and  draw  a  line  between  them.  With  a  pair  of  dividers  and  with 


ELEMENTARY   MACHINE   SHOP    PRACTICE  31 

C  and  D  as  centers  describe  the  arcs  which  locate  E  and  F.  The 
line  through  these  two  points  will  be  at  right  angles  with  CD  and 
at  its  center. 

Next  mark  with  the  dividers  on  each  side  of  CD  half  of  the  total 
distance  between  the  centers  of  holes  and  draw  GH  and  IJ.  From 
EF  mark  off  on  these  lines  the  required  spacing  of  the  holes  K,  L, 
M,  and  N. 

To  prove  that  the  hole  centers  are  laid  out  square,  measure  the 
distance  from  L  to  M  and  from  K  to  N  with  the  dividers.  Check 
the  layout  with  a  rule  to  see  if  the  centers  are  the  correct  distances 
apart. 

When  the  intersections  are  in  the  right  positions  for  the  hole 
centers,  mark  them  with  a  small  center  punch.  Now  scribe  circles 
about  these  points  a  little  larger  than  the  size  of  the  holes  to  be 
drilled  so  that  after  drilling  it  may  be  seen  if  the  hole  is  in  the  right 
position. 

Holding  the  Work. — This  exercise  being  small  in  comparison 
with  the  holes  to  be  drilled,  should  be  clamped  to  the  table  of  the 
drill  press,  Fig.  37,  or  held  in  a  drill  vise,  Fig.  38.  When  the 
former  method  is  used,  the  work  should  be  placed  so  that  the  drill 
is  above  one  of  the  slotted  holes  in  the  table.  The  object  in  this 
is  to  avoid  drilling  into  the  table.  In  using  the  vise,  the  parallels 
should  not  be  directly  under  the  drill. 


Fig.  37  Fig.  38 

If  the  holes  were  small,  say  less  than  1/4  inch,  or  the  casting 
larger,  it  could  be  held  by  hand.  In  this  case  the  work  should 
rest  on  a  piece  of  wood.  Since  the  wood  is  soft  the  work  is  less 
liable  to  slip  out  of  the  hand  than  when  placed  on  the  smooth  sur- 
face of  the  drill  press  table.  The  slipping  does  not  usually  occur 
until  the  point  of  the  drill  pierces  through  at  the  end  of  the  hole. 
Then  it  will  slip  unless  held  firmly. 


32 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


Selecting  the  Drill.— Drills  are  usually  designated  by  their  size 
and  the  shape  of  their  shanks.  The  size  refers  to  the  diameter  of 
the  drill.  The  shank  is  the  end  of  the  drill  by  which  it  is  held  in 
the  machine. 

The  common  drill  sizes  as  listed  in  most  catalogues  run  from 
1/16  of  an  inch  to  3  inches,  varying  by  1/64  inch.  The  sizes  usually 
found  in  shops,  however,  run  about  as  follows:  1/16"  to  1/2"  by 
1/64",  1/2"  to  1"  by  1/32",  1"  to  2"  by  1/16". 

Drills  are  also  made  in  number  and  letter  sizes.  The  number 
sizes  run  from  No.  1,  which  is  .2280  in  diameter,  to  No.  80,  which 
is  .0135  in  diameter.  There  are  80  different  sizes.  The  letter  drills 
range  from  A,  with  a  diameter  of  .234  inches,  to  Z,  which  is  .413  in 
diameter,  and  are  26  in  number. 

The  shank  of  the  common  drill  is  either  straight  or  tapered. 
When  straight  it  is  held  in  the  machine  with  a  drill  chuck. 


Fig.  39 

Taper  shank  drills  are  held  in  the  spindle  as  shown  in  Fig.  39. 
The  tongue,  or  tang,  of  the  drill,  A,  fits  into  a  slot  at  the  end  of  the 
hole  in  the  spindle  and  makes  the  drill  rotate  with  the  spindle.  The 
tapered  shank  keeps  the  drill  from  dropping  out.  To  remove  the 
drill  from  the  spindle,  a  taper  drift,  B,  is  used  as  shown. 

The  advantages  of  the  taper  shank  drill  are  that  it  runs  true  and 
is  more  conveniently  held  in  the  machine  for  large  sized  holes. 
Straight  shank  drills  larger  than  3/4"  must  be  held  in  a  chuck  so 
large  that  it  often  interferes  with  the  drilling. 

In  most  shops  drills  up  to  3/16"  diameter  are  used  with  straight 
shanks  and  those  from  3/16"  to  3/4"  in  diameter  with  either 
straight  or  taper  shanks.  Drills  larger  than  3/4"  in  diameter  usually 
have  taper  shanks. 


ELEMENTARY   MACHINE    SHOP    PRACTICE 


33 


Straight  shank  drills  cost  less  than  those  with  taper  shanks  and 
are  therefore  used  whenever  possible. 


Fig.  40 

The  steel  sleeve  or  bushing  shown  in  Fig.  40  is  used  when  the 
shank  of  a  taper  shank  drill  is  smaller  than  the  hole  in  the  spindle 
of  the  machine.  Sometimes  when  using  small  drills  in  a  large  ma- 
chine it  is  necessary  to  use  two  or  three  of  these  sleeves. 

After  selecting  the  drill  examine  the  edges.  If  they  are  dull 
sharpen  them  on  the  grinding  wheel. 

How  the  Drill  Should  Be  Ground. — The  common  twist  drill 
has  two  cutting  edges  A  and  B,  Fig.  41.  Like  other  tools  these 
must  be  ground  with  clearance  C  in  order  to  cut  when  the  drill  is 
forced  into  the  metal  and  rotated  as  indicated  by  the  arrow. 

The  cutting  edges  A  and  B  should  each  make  an  angle  of  59° 
with  the  axis  of  the  drill.  They  should  be  of  equal  length  in  order 
to  bring  the  point  of  the  drill  in  the  center.  If  the  point  is  off 
center,  only  one  edge  of  the  drill  will  cut.  This  not  only  reduces 
its  efficiency  but  also  produces  a  hole  larger  than  it  is  intended. 


Fig.  41  Fig.  42 

There  are  two  methods  of  sharpening  a  drill,  by  machine  and  by 


34 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


hand.     In  shops  where  a  great  deal  of  drilling  is  required,  a  drill 
grinding  machine  is  used. 

Hand  Grinding. — When  it  is  necessary  to  sharpen  a  drill  by 
hand,  and  especially  one  that  is  larger  than  3/8",  a  drill  grinding 
gauge  should  be  used,  Fig.  42. 

The  cutting  edge  on  smaller  drills  may  be  gauged  by  eye.  If 
the  side  of  the  grinding  wheel  is  used  instead  of  the  periphery,  it  is 
easier  to  produce  a  good  cutting  edge. 

Speed  of  Drill. — The  speed  of  the  drill  depends  upon  its  size, 
the  material  being  drilled  and  the  feed  used. 

The  following  table  will  give  beginners  some  idea  of  the  range 
of  speeds  for  different  sized  drills  made  of  carbon  steel. 


Diameter 
of 
Drill 

Revolutions  per  minute 

Soft  Steel 

Cast  Iron 

Brass 

1/8 

1/4 
3/8 
1/2 
3/4 

850 
390 
265 
200 
112 

1190 
565 
370 
260 
168 

1770 
855 
370 
412 

265 

Machinists  do  not,  as  a  rule,  consult  a  table  for  drill  speeds  be- 
cause the  hardness  of  the  material  varies,  and  drilling  machines  are 
not  usually  calibrated  for  the  spindle  speeds.  It  will  therefore  re- 
quire some  practical  experience  before  a  beginner  can  properly 
determine  the  speeds  for  different  sizes  of  drills. 

Centering  the  Drill. — There  are  two  common  methods  used  for 
centering  the  drill  in  piece  A.  In  either  case  the  center  punch  mark 
must  be  enlarged  to  about  1/16  inch  in  diameter. 

The  first  method  is  to  drill  a  small  hole  about  1/8  inch  in  diam- 
eter and  3/16  deep.  This  hole  acts  as  a  guide  for  the  1/2"  drill 
and  insures  its  being  in  the  correct  position. 

In  the  second  method  a  1/2"  drill  is  used  to  make  a  countersink 
in  the  work  about  1/4"  in  diameter.  If  this  countersink  is  not  in 
the  center  of  the  circle,  chip  a  small  groove  on  the  side  that  is 
farthest  from  it,  as  in  Fig.  43,  with  a  round  nose  chisel  or  center 


ELEMENTARY    MACHINE    SHOP    PRACTICE  35 

gouge.     Drill  a  little  deeper  and  if  the  countersink  still  does  not 
center,  repeat  the  operation. 


Fig.  43 

In  either  method  the  drill  must  be  centered  before  it  cuts  to  its 
full  size. 

Laying  Off  Holes  in  Piece  B. — After  the  holes  have  been 
drilled  in  piece  A  place  it  in  position  on  B.  With  a  scriber  lay  out 
the  circles  on  B  by  marking  through  the  holes  in  A. 

Drilling  Piece  B. — The  holes  in  piece  B  should  be  drilled  a  little 
larger  than  the  diameter  at  the  bottom  of  the  threads  of  a  1/2"  tap. 
This  is  13/32  of  an  inch. 

Center  punch  the  center  of  the  circles  as  accurately  as  possible 
by  eye.  The  drill  should  be  centered  by  the  second  method  de- 
scribed above. 

Drilling  a  Fixed  Depth. — The  desired  depth  of  hole  may  be 
obtained  with  the  aid  of  the  graduations  on  the  spindle  of  the  drill 
press.  In  case  the  spindle  is  not  calibrated  a  mark  may  be  made  on 
it  with  a  piece  of  chalk  to  indicate  when  the  desired  depth  has  been 
reached. 

Tapping. — Clamp  the  work  in  the  bench  vise  and  tap  the  holes, 
first  using  a  1/2"  plug  tap,  then  a  1/2"  bottoming  tap. 

The  plug  tap  is  started  by  pressing  down  on  it  and  turning  it 
with  a  wrench.  After  the  tap  has  entered  deep  enough  to  cut  a  full 
thread,  in  this  case  about  5/16"  deep,  it  is  no  longer  necessary  to 
press  down  on  it  as  the  tap  will  then  draw  into  the  work  when 
turned. 

Lard  oil  should  be  used  for  lubrication  when  tapping  cast  iron 
or  steel.  Brass  is  usually  tapped  dry. 

The  accuracy  with  which  a  hole  is  tapped  depends  upon  the 
operator,  as  the  tap  will  not  follow  the  hole.  The  tap  should  there- 
fore be  started  square  with  the  face  of  the  work.  In  some  cases 


36 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


this  may  be  judged  by  eye,  but  it  is  usually  necessary  for  beginners 
to  use  a  square  or  the  blade  of  a  square,  as  in  Fig.  44.  In  this  case 
the  blade  is  placed  back  of  the  tap  and  away  from  the  hole.  The 
tap  is  squared  up  by  bringing  its  shank  parallel  with  the  edge  of 
the  blade.  If  the  blade  were  placed  over  the  edge  of  the  hole,  the 
small  ridge  produced  by  the  tap  would  tip  it  out  of  square.  The  tap 
must  be  squared  before  it  cuts  to  its  full  diameter  as  any  attempt  to 
straighten  it  after  that  is  liable  to  break  it. 


\ 


Fig.  44 

As  the  plug  tap  is  tapered  at  the  end,  it  will  not  cut  the  full  size 
of  thread  to  the  bottom  of  the  hole.  It  is  desirable  on  account  of 
strength  to  have  the  length  of  the  full  threads  greater  than  the  diam- 
eter of  the  screw.  The  tapping  should  therefore  be  finished  with  a 
bottoming  tap  which  will  cut  full  threads  nearly  to  the  bottom  of  the 
hole. 

The  reason  for  not  using  the  bottoming  tap  for  the  entire  tap- 
ping operation  is  that  it  is  practically  impossible  to  start  such  a  tap. 

Filing  Holes  in  Piece  A. — In  case  the  holes  in  piece  B  do  not 
match  up  exactly  with  those  in  A,  the  screws  will  bind  or  will  not  go 
in  at  all.  It  is  then  necessary  to  file  the  holes  in  A  with  a  round  file 
until  the  screws  no  longer  bind. 


PART  III. 


MILLING  MACHINE  WORK 


ELEMENTARY   MACHINE   SHOP    PRACTICE  37 


MILLING  MACHINE  WORK 

There  are  several  different  kinds  of  milling  machines,  but  the 
ones  most  commonly  used  are  the  plain  miller  and  the  universal 
miller.  Both  of  these  machines  have  horizontal  spindles.  The  dif- 
ference between  them  is  that  the  table  of  the  plain  miller  can  be 
moved  only  at  fight  angles  or  parallel  to  the  spindle,  while  the  table 
of  the  universal  miller  may  be  moved  at  different  angles.  The  prin- 
cipal advantage  of  the  universal  machine  occurs  in  cutting  spiral 
gears,  spiral  milling  cutters,  etc.  As  this  class  of  work  will  not  be 
treated  in  this  book  only  the  plain  milling  machines  will  be  con- 
sidered. 

As  in  the  case  of  lathes  there  are  several  makes  of  millers,  all 
of  which,  although  varying  in  efficiency  and  utility,  employ  the  same 
fundamental  cutting  operations.  When  one  has  become  familiar 
with  the  operation  of  one  machine,  he  should  be  able  to  operate 
other  makes  of  different  design  with  very  little  difficulty. 

I 
CONE-DRIVEN  PLAIN  MILLER 

The  plain  miller  shown  in  Fig.  45  has  a  three  step  cone  drive 
with  double  back  gears.  The  small  pilot  wheel,  below  the  name  and 
index  plate,  together  with  the  two  levers  on  either  side  of  it  are 
used  for  changing  the  feed.  The  double-ended  V-shaped  lever  under 
the  table  is  for  starting  and  stopping  the  feed.  The  hand  crank 
and  hand  wheels  at  the  right  are  for  the  hand  feeds  and  for  raising 
and  lowering  the  table. 

HIGH-POWER  PLAIN  MILLER 

Fig.  46  shows  a  plain  miller  in  which  the  spindle  speed  changes 
are  obtained  by  shifting  encased  gears  near  the  driving  pulley.  This 
is  done  by  means  of  the  small  pilot  wheel  and  levers  on  the  gear 
box  below  the  name.  The  long  hand  lever  at  the  right  of  this  box 
operates  the  clutch  for  starting  and  stopping  the  machine. 


38 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


Fig.  45 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


39 


Fig.  46 


40 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


EXERCISE  NO.  8 


Cast   Iron 


C   T 


Fig.  47 

Sequence  of  Operations: 

1.     Grind  off  all  gates,  fins,  sand,  etc. 
Clamp  in  vise  and  mill  side  A. 
Mill  sides  B  and  C  square  with  A. 
Mill  side  D  parallel  to  A. 
Mill  both  ends  square  with  the  other  sides. 


2. 
3. 

4. 

5. 


Object  of  Grinding  Rough  Casting. — The  outer  surface  of  cast 
iron  is  hard  and  more  or  less  covered  with  sand.  This  would  dull 
milling  cutters  even  more  quickly  than  it  would  a  lathe  or  planer 
tool.  As  milling  cutters  are  expensive  and  require  more  time  to 
sharpen,  greater  care  should  be  taken  to  protect  their  cutting  edges. 
It  is  not  necessary,  however,  to  remove  all  of  the  scale,  but  the  cast- 
ing should  be  thoroughly  cleaned. 


Fig.  48 
Milling  Machine  Vise. — Fig.  48  shows  the  vise  used  in  the  mill- 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


41 


ing  machine.     It  has  a  graduated  swivel  base  so  that  it  can  be 
turned  at  different  angles. 

Clamping  the  Work. — The  work  is  held  in  the  milling  machine 
vise  as  shown  in  Fig.  49.  It  should  rest  on  two  parallels  that  are 
wide  enough  to  bring  the  surface  to  be  milled  above  the  level  of  the 
vise.  In  order  to  get  a  tighter  grip  on  it,  heavy  paper  should  be 
placed  between  it  and  the  jaws  of  the  vise.  The  paper  will  also 
protect  the  jaws  from  being  marred  by  the  rough  sides  of  the 
casting. 


Fig.  49 

The  Cutter. — Work  of  this  sort  is  milled  with  a  common  spiral 
milling  cutter.  As  these  cutters  are  made  in  different  lengths,  one 
should  be  selected  that  is  a  little  longer  than  the  widest  surface  to 
be  cut. 

The  Arbor. — All  milling  machine  arbors  are  provided  with  col- 
lars, Fig.  49,  of  different  lengths,  so  that  the  position  of  a  cutter  on 
them  may  be  varied.  These  collars  slip  loosly  on  over  the  arbor  and 
when  the  nut  A  is  tightened  clamp  the  cutter  in  place. 

If  the  cutter  is  mounted  near  the  main  bearing  of  the  milling 
machine  spindle,  it  will  work  better  than  if  located  near  the  outer 
end. 

One  end  of  the  arbor  is  tapered  and  fits  into  the  spindle  B.  It 
may  be  withdrawn  by  tightening  the  nut  C.  The  end  D  is  supported 
by  an  out  port  bearing. 

Most  arbors  are  also  provided  with  a  keyway  so  that  wlien 
heavy  cuts  are  to  be  taken  or  a  large  cutter  used  it  may  be  keyed 
to  the  arbor. 

Caution. — Beginners  are  cautioned  to  be  sure  that  the  direction 
of  rotation  and  speed  of  the  cutter  and  the  direction  of  the  feed  are 
correct  before  starting  a  cut. 


42  ELEMENTARY    MACHINE    SHOP    PRACTICE 

Direction  of  Cutter  Rotation. — Milling  cutters  are  all  ground 
with  clearance  A,  Fig.  50,  and  if  rotated  in  the  wrong  direction  will 
not  cut.  Therefore,  before  mounting  the  cutter  start  the  machine 
and  note  the  direction  of  rotation  of  the  arbor.  If  it  rotates  as  indi- 
cated by  the  arrow  the  cutter  should  be  mounted  as  shown.  If  the 
cutter  were  mounted  as  in  Fig.  51  it  would  not  cut. 


Fig.  50  Fig.  51 

Cutter  Speed. — The  proper  cutting  or  surface  speed  of  a  milling 
cutter  made  of  carbon  steel  is  about  60  to  70  feet  per  minute  when 
cutting  cast  iron.  Cutting  speed  is  the  velocity  of  a  point  on  the  cir- 
cumference of  the  cutter.  Thus  a  cutter  21/2  inches  in  diameter, 
and  turning  90  revolutions  per  minute,  will  have  a  cutting  speed  of 
about  60  feet  per  minute. 

No  fixed  rule  can  be  given  for  the  proper  cutter  speed  as  too 
much  depends  on  the  character  of  the  work,  the  hardness  of  the 
metal,  the  size  of  the  machines,  etc.  Machinists  determine  the 
proper  speeds  by  the  action  of  the  cutting  tool  and  from  previous 
experiences  on  work  similar  in  character. 

It  will  be  necessary  for  the  instructor  to  designate  the  speed  of 
the  machine  until  the  student  has  had  sufficient  practice  to  be  able 
to  judge  fairly  well  for  himself.  It  is  better  to  run  the  cutter  too 
slow  than  too  fast,  for  if  it  is  run  too  fast  it  will  soon  be  ruined. 

Direction  of  Feed. — The  direction  of  the  feed  in  relation  to  the 
cutter  rotation  is  very  important.  Fig.  52  shows  the  correct  way. 
In  this  case  the  direction  of  the  feed  is  opposite  to  the  rotation  of  the 
cutter.  The  wrong  way  is  shown  in  Fig.  53.  If  the  work  were  fed 
in  this  manner,  the  cutter  would  act  as  a  feed  roller  and  draw  the 
work  in  faster  than  it  would  cut.  This  would  break  the  teeth  of  the 
cutter. 

Roughing  Cut. — The  roughing  cut  on  cast  iron  should  always 
be  deep  enough  to  get  under  the  scale ;  in  this  case  about  3/32  or 
1/8  inch  deep.  Cast  iron  and  brass  are  milled  dry  but  on  steel  the 
cutter  works  better  if  lard  oil  or  some  other  lubricant  is  used. 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


43 


Fig.  52  Fig.  53 

Rate  of  Feed. — As  in  the  case  of  the  cutter  speed  no  fixed  rule 
can  be  given  for  the  rate  of  feed.  This  should  be  determined  by 
the  instructor.  It  may  be  stated,  however,  that  .018  of  an  inch 
feed  per  revolution  of  the  cutter  should  be  safe  in  this  case.  If  a 
good  machine  is  used  and  the  iron  is  soft  this  feed  could  be  in- 
creased. 

Finishing  Cut. — The  depth  of  the  finishing  cut  can  be  anything 
up  to  1/32  of  an  inch.  If  more  than  this  is  taken  off,  the  surface 
may  not  be  uniform.  The  same  cutter  speed  as  for  roughing  can 
be  maintained  but  the  feed  should  be  increased.  If  a  large  surface 
is  to  be  finished  and  the  iron  is  soft  it  will  pay,  in  the  amount  of 
time  saved,  to  increase  both  the  speed  and  the  feed. 

After  side  A,  Fig.  47,  is  finished,  the  sides  B  and  C  are  milled 
square  with  A.  D  is  then  milled  parallel  with  A.  The  method  of 
clamping  the  work  in  the  vise  is  practically  the  same  as  that  used 
for  the  shaper  work. 


Fig.  54 

Milling  the  Ends. — If,  in  milling  the  ends,  the  block  extends 
so  far  above  the  jaws  of  the  vise  that  the  action  of  the  cutter  has  a 
tendency  to  tip  it,  turn  the  vise  through  90  degrees  and  clamp  it 
edgewise  as  shown  in  Fig.  54. 


44 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


EXERCISE  NO.  9 


Fig.  55 


Sequence  of  Operations: 


1.  Mill  the  recess  A  and  the  slot  B  with  a  5/8"  end  mill. 

2.  Mill  the  corners  D  and  E  with  a  side  milling  cutter. 

3.  Mill  the  grooves  in  the  bottom  with  a  3/8"  milling  cutter. 

4.  Mill  the  concave  sides  with  a  forming  cutter. 

Milling  the  Recess  and  Slot. —  (Exercise  No.  8  is  to  be  used 
for  this  exercise.)  The  recess  A  and  the  slot  B  are  good  examples 
of  the  kind  of  work  for  which  the  end  mill  is  particularly  adapted. 
However,  this  tool  is  also  used  for  other  kinds  of  work. 


Fig.  56 


The  end  mill,  Fig.  56,  has  a  taper  shank  and  is  mounted  in  the 
spindle  of  the  milling  machine  in  the  same  manner  as  a  drill  in  a 
drill  press.  These  shanks  have  either  the  Morse  taper  or  the  Brown 
and  Sharp  taper.  The  Morse  standard  taper  is  used  for  drills  as 
well  as  for  end  mills.  The  taper  of  the  Brown  and  Sharp  standard 
is  less  than  the  Morse  standard.  For  this  reason  the  shanks  of 
end  mills  used  in  milling  machines  usually  have  the  Brown  and 
Sharp  taper  as  they  will  stay  in  the  spindle  better. 


ELEMENTARY   MACHINE    SHOP    PRACTICE 


45 


Fig.  57 

Clamping  the  Work. — Lay  off  the  outline  of  the  recess  on  the 
surface  of  the  block  and  clamp  it  square  in  the  vise  as  in  Fig.  57. 
Adjust  the  position  of  the  block  until  the  end  of  the  mill  is  just 
touching  the  surface  at  one  corner  of  the  recess.  In  order  to  de- 
termine when  the  recess  has  been  cut  to  the  full  depth,  set  the  dial 
on  the  cross  slide  to  the  zero  point.  This  dial  is  graduated  in  thou- 
sandths of  an  inch. 

Depth  of  Cut. — Force  the  end  of  the  mill  into  the  surface  for 
about  .03  of  an  inch  and  feed  the  work  by  hand  so  that  the  mill  will 
cut  just  inside  of  the  outline  marked.  Repeat  this  operation  until 
the  cross-feed  dial  reads  .250  of  an  inch,  the  required  depth  of  the 
recess. 

End  mills  usually  work  better  with  shallow  cuts  and  coarse  feeds 
than  with  deep  cuts  and  fine  feeds.  Another  reason  for  taking  shal- 
low cuts  in  this  case  is  because  there  are  no  teeth  at  the  center  of 
the  cutting  end  A,  Fig.  56.  This  makes  it  hard  to  force  the  tool 
into  the  metal. 

Speed  of  Cutter. — As  this  cutter  is  much  smaller  in  diameter 
than  the  spiral  mill  used  in  exercise  No.  8  the  spindle  speed  may  be 
increased. 

Milling  the  Slot. — The  slot  is  to  be  milled  with  the  same  end 
mill  that  was  used  for  cutting  the  recess.  Before  starting  this  cut, 
remove  the  work  from  the  vise  and  drill  a  1/2  inch  hole  as  shown  at 
H,  Fig.  58.  This  hole  is  necessary  on  account  of  the  center  of  the 
end  mill  having  no  teeth. 

After  reclamping  the  work  in  the  vise  adjust  it  so  that  the  mill 
will  be  at  the  end  of  the  slot  where  the  hole  has  been  drilled.  Feed 
the  cutter  through  the  block,  Fig.  59,  as  far  as  the  cutting  edges 
will  permit.  It  cuts  better  in  this  position  than  at  the  outer  end. 


46 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


Fig.  58 


Fig.  59 


Now  feed  the  work  horizontally  until  the  cutter  reaches  the  other 
end  of  the  slot. 

Rate  of  Feed. — If  the  automatic  feed  is  used  it  should  be  very 
fine.  The  safest  way  for  beginners  is  to  feed  it  by  hand.  If  too 
coarse  a  feed  is  used  the  cutter  will  break. 

Direction  of  Feed. — When  cutting  a  slot  like  this  where  half 
of  the  circumference  of  the  mill  is  in  contact  with  the  metal  and 
when  using  the  end  of  the  mill  as  in  cutting  the  recess,  the  feed 
may  be  in  either  direction. 

Gang  Milling. — When  two  or  more  cutters  are  used  on  one 
spindle  at  the  same  time  it  is  called  gang  milling.  The  corners  E 
and  D  of  this  exercise  may  be  milled  by  first  cutting  one  and  then 
the  other  with  a  side  milling  cutter.  A  simpler  method  would  be  to 
use  two  cutters,  Fig.  60,  with  the  collar  I  between  them  so  that  they 
will  be  the  proper  distance  apart. 


Fig.  60 

A  third  method  is  to  use  a  cutter  between  the  side  mills  instead 
of  a  collar.  If  this  method  is  used  the  surface  should  not  be  milled 
when  squaring  the  block  in  exercise  No.  8. 

Depth  of  Cut. — When  using  gang  cutters  the  required  depth  is 
usually  cut  at  one  time.  To  set  the  work  for  the  depth  shown  in 
Fig.  55,  bring  the  work  up  under  the  revolving  cutter  until  it  just 
touches.  Then  move  the  work  clear  of  the  cutter  and  raise  it  3/16 
or  .187  of  an  inch,  using  the  graduated  dial  on  the  elevating  shaft. 


ELEMENTARY   MACHINE    SHOP    PRACTICE  47 

Cutting  Speed. — The  speed  of  the  machine  for  gang  cutting  is 
determined  by  the  diameter  of  the  largest  cutter. 

Groove  Cutting. — The  two  3/8  inch  grooves  in  this  exercise 
may  be  cut  with  one  or  two  keyway  cutters. 

The  difference  between  this  cutter  and  the  side  milling  cutter  is 
that  it  has  no  cutting  edges  on  the  side.  It  is  used  principally  for 
cutting  grooves  like  these  and  for  cutting  standard  keyways  in 
shafts. 

Forming  Cutters. — Cutters  having  curved  or  irregular  cutting 
edges  are  usually  called  formed  cutters.  The  one  used  for  the  con- 
cave surface  in  this  exercise  might  be  classed  as  such,  but  is  usually 
called  a  convex  cutter. 

When  cutting  the  concave  surface  in  the  end  of  the  block  it  will 
be  less  liable  to  slip  if  clamped  edgewise  in  the  vise. 


48 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


DIVIDING  HEAD  AND  TAILSTOCK 


Fig.  61 

Fig.  61  shows  a  dividing  head  and  tailstock.  The  tailstock  is 
used  for  holding  the  ends  of  shafts,  mandrels,  etc.  The  small  jack 
shown  is  for  supporting  the  middle  of  long  slender  work  when 
mounted  between  the  centers. 

The  Dividing  Head. — The  dividing  head  is  used  for  accurately 
spacing  or  dividing  the  circumference  of  a  piece  of  work  into  any 
number  of  parts,  as  in  squaring  a  shaft,  gear  cutting,  etc. 

The  center  and  slotted  arm  are  made  in  one  piece  and  like  a  lathe 
center  are  held  in  the  spindle  of  the  dividing  head  by  a  taper  fit. 
The  slot  in  the  arm  is  to  receive  the  tail  of  a  lathe  dog  so  that  work 
mounted  between  the  centers  will  rotate  with  the  spindle  of  the 
dividing  head.  The  set  screw  at  the  end  of  the  slot  is  to  take  up 
the  slack  or  lost  motion  between  the  sides  of  the  slot  and  the  tail 
of  the  lathe  dog. 

The  spindle  of  the  dividing  head  is  threaded  like  a  lathe  spindle 
so  that  a  chuck  may  be  screwed  on  it. 

The  Index  Plate. — The  round  plate  with  a  number  of  circles  of 
holes  on  the  side  of  the  dividing  head  is  called  the  index  plate. 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


49 


Index  Crank. — The  index  crank  is  in  front  of  the  index  plate 
and  is  provided  with  a  slot  so  that  by  loosening  the  hexagonal  nut 
at  the  center  it  may  be  moved  to  different  positions. 

Index  Pin. — At  the  end  of  the  index  crank  is  the  index  pin. 
One  end  of  this  pin  is  of  such  size  that  it  just  fits  into  the  holes  in 
the  index  plate.  The  other  end  has  a  knurled  knob  which  is  used 
to  withdraw  the  pin  so  that  the  crank  may  be  turned. 

Indexing. — The  shaft  on  which  the  index  crank  is  mounted  is 
geared  to  the  spindle  of  the  dividing  head  at  a  ratio  of  40  to  1. 
Therefore,  40  turns  of  the  crank  will  cause  the  spindle  to  make  one 
complete  revolution. 

If  it  were  desired  to  make  4  divisions,  as  in  squaring  a  shaft,  the 
number  of  turns  of  the  crank  would  be  40  -=-  4,  or  10  revolutions  for 
each  cut.  To  make  40  divisions  as  in  a  40-tooth  gear  wheel  the 
crank  would  be  turned  one  revolution  for  each  tooth. 

In  case  32  divisions  are  to  be  made,  the  turns  of  the  crank  per 
division  would  be  40/32  or  1  1/4  revolutions.  To  turn  the  crank 
1/4  of  a  revolution  a  circle  of  holes  is  selected  that  is  evenly  divided 
by  4  as  24,  36,  etc.  If  the  24  hole  circle  is  used,  the  crank  should  be 
turned  6  holes  exclusive  of  the  hole  the  index  pin  is  in.  Therefore 
to  make  one  of  the  32  divisions  the  index  crank  is  turned  1  revolu- 
tion plus  6  holes  on  the  24  hole  circle. 

The  Sector. — All  dividing  heads  are  provided  with  a  sector 
which  eliminates  counting  the  holes  in  the  index  plate  each  time  a 
division  is  made. 


By  loosening  the  screw  A,  Fig.  62, 
the  arms  D  and  E  may  be  adjusted  to  in- 
clude any  desired  number  of  holes.  Thus 
to  turn  the  index  crank  1/4  of  a  revolu- 
tion on  a  24  hole  circle  the  index  pin 
should  be  rotated  from  B  to  C. 


Fig.  62 


50 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


Fig.  63 


Examples  of  Use  for  the  Dividing  Head. — Fig.  63  shows  the 
method  of  cutting  five  equally  spaced  slots  on  the  circumference  of  a 
circular  plate.  The  latter  is  mounted  on  a  mandrel  such  as  is 
used  in  cutting  gears.  The  method  of  supporting  the  outer  end  of 
this  mandrel  is  clearly  shown.  The  cutter  used  is  a  side  cutting 
miller. 

An  example  of  accurate  indexing  is  shown  in  Fig.  64.  Thirty-six 
1/4  inch  holes  are  to  be  equally  spaced  on  the  circumference  of  a 
19-inch  disc.  They  are  first  drilled  with  a  short  drill  a  little  under 
size  and  are  then  finished  to  size  with  a  1/4-inch  end  mill. 

This  figure  also  shows  the  method  of  handling  work  larger  than 
the  dividing  head  will  swing  when  the  spindle  is  in  the  horizontal 
position.  In  this  case  the  dividing  head  spindle  has  been  turned 
through  an  angle  of  90°. 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


51 


Fig.  64 


52  ELEMENTARY   MACHINE    SHOP    PRACTICE 


SPUR  GEARS  AND  RACK 

Gears  whose  tooth  elements  are  parallel  with  their  axis  are 
known  as  spur  gears.  They  are  also  called  straight  faced  gears. 

There  are  several  different  systems  of  gear  teeth  outlines,  but 
the  one  most  commonly  used  is  the  involute  system.  This  system 
requires  only  eight  cutters  for  each  pitch  and  has  a  wide  application. 

The  operator  of  a  milling  machine  should  become  familiar  with 
the  following  terms :  the  pitch  circle,  the  pitch  diameter,  the  circular 
pitch  and  the  diametral  pitch. 

Pitch  Circle. — The  size  of  a  gear  is  determined  by  the  pitch 
circle,  C,  Fig.  65. 


Rack 


Fig.  65 

Pitch  Diameter. — The  pitch  diameter  is  the  diameter  of  the 
pitch  circle,  D,  Fig.  65. 

Circular  Pitch. — The  circular  pitch  is  the  distance  from  the 
center  of  one  tooth  to  the  center  of  the  adjoining  tooth  measured  on 
the  pitch  circle,  B,  Fig.  65. 

Diametral  Pitch. — The  diametral  pitch  is  the  number  of  teeth 
per  inch  of  pitch  diameter.  It  therefore  determines  the  size  of  the 
teeth. 

For  example,  a  gear  with  12  teeth  and  a  pitch  diameter  of  2 
inches  will  have  a  diametral  pitch  of  6.  One  with  16  teeth  and  the 
same  pitch  diameter  will  have  a  diametral  pitch  of  8.  Of  these  two 
gears  the  teeth  on  the  16  tooth  gear  will  necessarily  be  smaller  than 
those  on  the  12  tooth  gear. 


ELEMENTARY    MACHINE    SHOP    PRACTICE  53 


The  distance  A,  Fig.  65,  is  the  reciprocal  of  the  diametral  pitch. 
Thus  on  an  8  diametral  pitch  gear,  the  distance  A  is  1/8  of  an  inch. 
The  diametral  pitch  will  hereafter  be  referred  to  as  the  pitch. 

Shape  of  Tooth. — The  thickness  of  the  tooth  on  the  pitch  circle 
is  the  same  in  all  sizes  of  gears  having  the  same  pitch.  The  shape 
of  the  tooth,  however,  varies  with  the  size  of  the  gear ;  that  is,  the 
curve  on  the  side  of  a  tooth  on  a  12  tooth  gear  is  a  little  different 
from  that  on  a  gear  having  13  teeth.  The  greatest  contrast  is  noted 
between  a  12  tooth  gear  and  a  rack,  Fig.  65. 

When  gear  wheels  are  cut  in  a  milling  machine  a  formed  cutter 
having  the  same  profile  as  the  space  between  the  teeth  is  used.  If 
it  were  necessary  to  cut  the  teeth  theoretically  correct,  a  different 
cutter  would  be  required  for  each  different  size  gear.  In  practice, 
however,  for  the  involute  system  only  8  cutters  are  used  for  each 
pitch.  The  following  table  gives  the  range  of  each  cutter. 

No.   1  will  cut  wheels  from  135  teeth  to  a  rack. 

"     2     "        "         "  "        55      "  134  teeth,  inclusive. 

"     3     "        "         "  "        35      "  54      " 

tt    ^     it       ft        ft          tt       25     "  34     "  " 

ft     c     tt        a         a          tt        21      "  oz      ft  ft 

ft       z       ft  ft  ft  ft  17        ft  orv        tt  ft 

tf    *J    ft       ft        tt          tt       -t  A      ft  \  (~\     (<  <( 

ft    O    ft       ft        ft          ft       1  O     ft  1-5     If  tt 

For  example,  if  it  is  desired  to  cut  a  10  pitch  gear  with  28  teeth, 
a  10  pitch,  number  4  cutter  should  be  used. 

Rack. — The  teeth  of  a  rack  are  developed  along  a  straight  line 
and  mesh  with  a  gear  having  the  same  pitch. 


54 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


EXERCISE  NO.  10 


10 


2. 
3. 

4. 

5. 


25  T.   12  P.    j-f'H 
Fig.  66 

GEAR  CUTTING 
Sequence  of  Operations: 

1.     Select  cutter  and  mount  on  milling  machine  arbor. 

Line  up  center  of  cutter  with  center  of  the  dividing  head. 

Place  gear  blank  on  mandrel  and  mount  mandrel  between 

centers  of  the  dividing  head  and  the  tail  stock. 

Set  cutter  to  proper  depth. 

Set  the   index   crank  and  sector  on  dividing  head  for  25 

divisions. 

Selecting  Cutter. — The  number  of  teeth  to  be  cut  in  this  gear  is 
25.  Referring  to  the  table  on  page  53  it  is  seen  that  a  number  5 
cutter  has  the  proper  range. 

Mounting  Cutter. — The  cutter  is  mounted  on  the  milling  ma- 
chine arbor  as  close  to  the  main  bearing  of  the  spindle  as  possible 
and  yet  far  enough  away  to  have  it  line  up  with  the  center  of  the 
dividing  head. 

Centering  Cutter. — In  order  to  cut  the  teeth  radially  the  center 
of  the  cutter  must  be  in  line  with  the  center  of  the  dividing  head. 
All  gear  cutters  are  marked  with  a  center  line  so  that  by  moving  the 
dividing  head  close  to  the  cutter  and  adjusting  the  position  of  the 
table  they  may  be  accurately  centered. 

Placing  Gear  on  Mandrel. — Gear  blanks  are  usually  mounted 
on  a  gear  mandrel,  Fig.  67. 


Fig.  67 


ELEMENTARY    MACHINE    SHOP    PRACTICE  55 

This  mandrel  is  not  tapered,  the  clamping  being  done  by  means 
of  the  nut  A.  By  removing  the  collars  B  B  several  gears  can  be 
mounted  at  one  time. 

Mounting  the  Gear  Mandrel. — A  milling  machine  dog  or  a 
lathe  dog  is  fastened  on  one  end  of  the  mandrel.  The  latter  is  then 
mounted  between  the  dividing  head  center  and  the  tail  stock  center 
in  very  much  the  same  manner  as  is  shown  in  Fig.  63.  Oil  should  be 
used  on  the  tail  stock  center.  The  set  screw  in  the  slotted  arm  of  the 
dividing  head  is  screwed  against  the  tail  of  the  dog  to  prevenr  any 
lost  motion. 

Depth  of  Cut. — When  cutting  gear  teeth  of  this  size  all  of  the 
stock  is  removed  at  one  cut.  For  gears  with  large  teeth,  say  of  4 
or  5  pitch  and  larger,  it  may  be  necessary  to  take  two  cuts. 

To  set  the  work  so  that  the  cutter  will  cut  the  proper  depth  start 
the  machine  and  raise  the  work  up  under  the  revolving  cutter  until 
it  just  touches.  Move  the  work  clear  of  the  cutter  and  set  the  dial 
on  the  elevating  shaft  to  zero.  Now  raise  the  table  .180  of  an  inch 
as  indicated  by  the  graduations  on  the  dial.  This  is  the  proper 
depth  for  a  12  pitch  gear  tooth. 

All  milling  machines  are  provided  with  a  chart  that  gives  the 
depth  to  be  cut  and  the  range  of  the  cutters  for  all  sizes  of  gears. 
This  side  of  each  cutter  is  also  marked  with  this  information  for  its 
particular  pitch  and  range. 

Setting  the  Index  Crank. — There  is  a  clamping  nut  on  the  side 
of  the  dividing  head  opposite  the  index  plate  which  should  al- 
ways be  loosened  before  turning  the  index  crank  and  tightened 
after  indexing.  In  order  to  index  25  teeth,  the  crank  must  be  turned 
1/25  of  40,  or  1  3/5  turns  per  tooth.  3/5  of  a  revolution  can  be 
measured  on  a  circle  of  holes  which  is  a  multiple  of  5  as  20,  25,  30, 
35,  etc.  Assuming  the  use  of  the  30  hole  circle,  3/5  of  a  revolution 
will  be  represented  by  18  spaces. 

Loosen  the  nut  B,  Fig.  68,  and  adjust  the  index  pin  C  in  one  of 
the  holes  of  the  30  hole  circle.  Now  tighten  the  nut  B  just  enough 
to  hold  the  crank  in  position  and  pull  out  the  index  pin  to  see  if  it 
will  drop  into  the  hole  without  binding.  If  the  index  pin  is  not  in 
line  with  the  hole  its  position  may  be  changed  slightly  by  rapping 
the  end  of  the  index  crank  with  a  piece  of  wood.  If  a  light  rap  is 
not  sufficient  loosen  the  nut  a  little.  After  the  index  pin  is  properly 
set,  tighten  the  nut  B  so  that  it  will  stay  in  this  position. 


56 


ELEMENTARY    MACHINE    SHOP    PRACTICE 


Fig.  68 

Setting  the  Sector. — Loosen  the  clamping  screw  A  on  the  sector, 
Fig.  68,  and  move  the  arm  D  so  that  the  beveled  edge  rests  against 
index  pin  C.  Withdraw  the  index  pin  and  turn  the  crank  to  the 
right  18  holes,  not  counting  the  hole  the  pin  was  in.  Without 
changing  the  position  of  the  arm  D  move  the  other  arm  E  until  its 
beveled  edge  strikes  the  index  pin  in  its  new  position  at  the  18th 
hole.  Tighten  the  screw  A.  The  sector  is  now  set  to  include  3/5 
of  a  turn,  or  18  spaces. 

Indexing. — Before  taking  the  first  cut,  turn  the  index  crank 
clockwise  one  complete  revolution.  This  will  take  out  all  the  slack 
or  lost  motion  in  the  dividing  head. 

To  index  the  gear  for  the  next  cut  rotate  the  sector  arm  D  up 
to  the  index  pin.  Withdraw  the  pin  and  give  the  crank  one  turn  to 
the  right  or  clockwise,  plus  the  fraction  of  a  turn  included  between 
the  sector  arms.  This  operation  is  repeated  until  the  gear  is  finished. 

Cutting  a  Rack. — The  size  of  the  teeth  of  a  rack,  as  with  spur 
gears,  is  designated  by  the  pitch. 


Fig.  69 


f  ELEMENTARY    MACHINE    SHOP    PRACTICE  57 

To  space  the  teeth  it  is  necessary  to  know  the  distance  from  the 
center  of  one  tooth  to  the  center  of  the  adjoining  one.  For  a  12 
pitch  rack  this  is  the  same  as  the  circular  pitch  of  12  pitch  spur 
gears.  The  circular  pitch  is  obtained  by  dividing  3.1416  by  the 
diametral  pitch.  With  a  diametral  pitch  of  12  the  circular  pitch  is 
.262".  The  following  table  gives  the  diametral  pitches  commonly 
used  and  the  corresponding  circular  pitches. 

Diametral  Circular  Diametral  Circular 

Pitch  Pitch  Pitch  Pitch 

\}/4  2.5133"  10  .314 

1%  2.0944  11  .286 

1#  17952  12  .262 

2  1.571  14  .224 
2y4  1.396  16  .196 
2%  1.257  18  .175 
2y4  1.142  20  .157 

3  1.047  22  .143 
3i/j                  .898  24  .131 

4  .785  26  .121 

5  .628  28  .112 

6  .524  30  .105 

7  .449  32  .098 

8  .393  36  .087 

9  .349  40  .079 

48  .065 

Clamp  the  rack  blank  in  the  milling  machine  vise  on  a  parallel 
as  shown  in  Fig.  69.  After  taking  the  first  cut  of  the  required  depth, 
set  the  dial  on  the  cross  feed  to  zero.  Move  the  table  horizontally 
.262"  as  indicated  by  the  dial  on  the  hand  crank.  Take  another  cut 
and  continue  this  operation  until  the  rack  is  finished.  If  one  end  of 
the  rack,  as  A,  extends  beyond  the  vise,  it  will  be  necessary  to  reset 
the  work  as  the  cutter  will  not  cut  satisfactorily  with  such  poor 
support. 


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